diff --git a/src/kit/taosdemo/taosdemo.c b/src/kit/taosdemo/taosdemo.c
index 482d76ebd5498f3e744b3313a0b5cfb7cee09d5c..88ff34991514212854aac3296bfd81a57e480f08 100644
--- a/src/kit/taosdemo/taosdemo.c
+++ b/src/kit/taosdemo/taosdemo.c
@@ -6717,7 +6717,7 @@ static int generateSampleFromRand(
 
                 case TSDB_DATA_TYPE_NCHAR:
                     dataLen = (columns)?columns[c].dataLen:g_args.binwidth;
-                    rand_string(data, dataLen);
+                    rand_string(data, dataLen - 1);
                     pos += sprintf(buff + pos, "%s,", data);
                     break;