diff --git a/src/kit/taosdemo/taosdemo.c b/src/kit/taosdemo/taosdemo.c
index 692f6c0345dc6526d9b93303a3bdc781980cf83f..bcdf97b3d5780c3e6eade3a5cad758845d69aa64 100644
--- a/src/kit/taosdemo/taosdemo.c
+++ b/src/kit/taosdemo/taosdemo.c
@@ -6388,7 +6388,7 @@ 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;