diff --git a/tests/system-test/2-query/interp.py b/tests/system-test/2-query/interp.py
index 7bf0191ec176c8a833eb3ff16fbb007e456fe93f..059513f737202bb35ce4a0cd9db5b53e154e7700 100644
--- a/tests/system-test/2-query/interp.py
+++ b/tests/system-test/2-query/interp.py
@@ -356,8 +356,227 @@ class TDTestCase:
         tdSql.query(f"select interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:16', '2020-02-01 00:00:19') every(1s) fill(linear)")
         tdSql.checkRows(0)
 
+        tdLog.printNoPrefix("==========step8:test _irowts with interp")
+
+        # fill null
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:08', '2020-02-01 00:00:12') every(500a) fill(null)")
+        tdSql.checkRows(9)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:08.500')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:09.500')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:10.500')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:11.500')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(null)")
+        tdSql.checkRows(13)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:04.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:06.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
+        tdSql.checkData(9, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(10, 0, '2020-02-01 00:00:14.000')
+        tdSql.checkData(11, 0, '2020-02-01 00:00:15.000')
+        tdSql.checkData(12, 0, '2020-02-01 00:00:16.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:05', '2020-02-01 00:00:15') every(2s) fill(null)")
+        tdSql.checkRows(6)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:15.000')
+
+        # fill value
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:08', '2020-02-01 00:00:12') every(500a) fill(value, 1)")
+        tdSql.checkRows(9)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:08.500')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:09.500')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:10.500')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:11.500')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(value, 1)")
+        tdSql.checkRows(13)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:04.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:06.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
+        tdSql.checkData(9, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(10, 0, '2020-02-01 00:00:14.000')
+        tdSql.checkData(11, 0, '2020-02-01 00:00:15.000')
+        tdSql.checkData(12, 0, '2020-02-01 00:00:16.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:05', '2020-02-01 00:00:15') every(2s) fill(value, 1)")
+        tdSql.checkRows(6)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:15.000')
+
+        # fill prev
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:08', '2020-02-01 00:00:12') every(500a) fill(prev)")
+        tdSql.checkRows(9)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:08.500')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:09.500')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:10.500')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:11.500')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(prev)")
+        tdSql.checkRows(12)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:06.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:12.000')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(9, 0, '2020-02-01 00:00:14.000')
+        tdSql.checkData(10, 0, '2020-02-01 00:00:15.000')
+        tdSql.checkData(11, 0, '2020-02-01 00:00:16.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:05', '2020-02-01 00:00:15') every(2s) fill(prev)")
+        tdSql.checkRows(6)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:15.000')
+
+        # fill next
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:08', '2020-02-01 00:00:12') every(500a) fill(next)")
+        tdSql.checkRows(9)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:08.500')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:09.500')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:10.500')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:11.500')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(next)")
+        tdSql.checkRows(12)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:04.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:06.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
+        tdSql.checkData(9, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(10, 0, '2020-02-01 00:00:14.000')
+        tdSql.checkData(11, 0, '2020-02-01 00:00:15.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:05', '2020-02-01 00:00:15') every(2s) fill(next)")
+        tdSql.checkRows(6)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:15.000')
+
+        # fill linear
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:08', '2020-02-01 00:00:12') every(500a) fill(linear)")
+        tdSql.checkRows(9)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:08.500')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:09.500')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:10.500')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:11.500')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:12.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:04', '2020-02-01 00:00:16') every(1s) fill(linear)")
+        tdSql.checkRows(11)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:06.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:08.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:10.000')
+        tdSql.checkData(6, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(7, 0, '2020-02-01 00:00:12.000')
+        tdSql.checkData(8, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(9, 0, '2020-02-01 00:00:14.000')
+        tdSql.checkData(10, 0, '2020-02-01 00:00:15.000')
+
+        tdSql.query(f"select _irowts,interp(c0) from {dbname}.{tbname} range('2020-02-01 00:00:05', '2020-02-01 00:00:15') every(2s) fill(linear)")
+        tdSql.checkRows(6)
+        tdSql.checkCols(2)
+
+        tdSql.checkData(0, 0, '2020-02-01 00:00:05.000')
+        tdSql.checkData(1, 0, '2020-02-01 00:00:07.000')
+        tdSql.checkData(2, 0, '2020-02-01 00:00:09.000')
+        tdSql.checkData(3, 0, '2020-02-01 00:00:11.000')
+        tdSql.checkData(4, 0, '2020-02-01 00:00:13.000')
+        tdSql.checkData(5, 0, '2020-02-01 00:00:15.000')
+
+        return
 
-        tdLog.printNoPrefix("==========step8:test intra block interpolation")
+        tdLog.printNoPrefix("==========step9:test intra block interpolation")
         tdSql.execute(f"drop database {dbname}");
 
         tdSql.prepare()
@@ -551,7 +770,7 @@ class TDTestCase:
         tdSql.checkData(0, 0, 15)
         tdSql.checkData(1, 0, 15)
 
-        tdLog.printNoPrefix("==========step9:test multi-interp cases")
+        tdLog.printNoPrefix("==========step10:test multi-interp cases")
         tdSql.query(f"select interp(c0),interp(c1),interp(c2),interp(c3) from {dbname}.{tbname} range('2020-02-09 00:00:05', '2020-02-13 00:00:05') every(1d) fill(null)")
         tdSql.checkRows(5)
         tdSql.checkCols(4)
@@ -601,7 +820,7 @@ class TDTestCase:
         for i in range (tdSql.queryCols):
             tdSql.checkData(0, i, 13)
 
-        tdLog.printNoPrefix("==========step10:test error cases")
+        tdLog.printNoPrefix("==========step11:test error cases")
 
         tdSql.error(f"select interp(c0) from {dbname}.{tbname}")
         tdSql.error(f"select interp(c0) from {dbname}.{tbname} range('2020-02-10 00:00:05', '2020-02-15 00:00:05')")