diff --git a/pkg/expression/expr_to_pb_test.go b/pkg/expression/expr_to_pb_test.go
index cd94586ab1..51d70bb9b0 100644
--- a/pkg/expression/expr_to_pb_test.go
+++ b/pkg/expression/expr_to_pb_test.go
@@ -1852,6 +1852,21 @@ func TestExprPushDownToTiKV(t *testing.T) {
 			retType:      types.NewFieldType(mysql.TypeDatetime),
 			args:         []Expression{stringColumn, NewStrConst("%h%y")},
 		},
+		{
+			functionName: ast.TimestampDiff,
+			retType:      types.NewFieldType(mysql.TypeLong),
+			args:         []Expression{NewStrConst("Second"), datetimeColumn, datetimeColumn},
+		},
+		{
+			functionName: ast.TimestampDiff,
+			retType:      types.NewFieldType(mysql.TypeLong),
+			args:         []Expression{NewStrConst("DAY"), datetimeColumn, datetimeColumn},
+		},
+		{
+			functionName: ast.TimestampDiff,
+			retType:      types.NewFieldType(mysql.TypeLong),
+			args:         []Expression{NewStrConst("year"), datetimeColumn, datetimeColumn},
+		},
 	}
 
 	ctx = mock.NewContext()
diff --git a/pkg/expression/infer_pushdown.go b/pkg/expression/infer_pushdown.go
index ea36c72a3e..ff1fa69127 100644
--- a/pkg/expression/infer_pushdown.go
+++ b/pkg/expression/infer_pushdown.go
@@ -210,7 +210,7 @@ func scalarExprSupportedByTiKV(ctx EvalContext, sf *ScalarFunction) bool {
 		/* ast.DayName */ ast.DayOfMonth, ast.DayOfWeek, ast.DayOfYear,
 		/* ast.Weekday */ ast.WeekOfYear, ast.Year,
 		ast.FromDays, /* ast.ToDays */
-		ast.PeriodAdd, ast.PeriodDiff /*ast.TimestampDiff, ast.DateAdd*/, ast.FromUnixTime,
+		ast.PeriodAdd, ast.PeriodDiff, ast.TimestampDiff, ast.FromUnixTime,
 		/* ast.LastDay */
 		ast.Sysdate, ast.StrToDate,
 
diff --git a/tests/integrationtest/r/expression/issues.result b/tests/integrationtest/r/expression/issues.result
index d285a669aa..eb784dd5dc 100644
--- a/tests/integrationtest/r/expression/issues.result
+++ b/tests/integrationtest/r/expression/issues.result
@@ -531,14 +531,14 @@ insert into t2 value (1,2,date'2020-05-08');
 explain format = 'brief' SELECT /*+ INL_MERGE_JOIN(t1,t2) */ COUNT(*) FROM  t1 LEFT JOIN t2 ON t1.id = t2.order_id WHERE t1.ns = 'a' AND t1.org_id IN (1) AND t1.status IN (2,6,10) AND timestampdiff(month, t2.begin_time, date'2020-05-06') = 0;
 id	estRows	task	access object	operator info
 StreamAgg	1.00	root		funcs:count(1)->Column#10
-└─IndexJoin	0.03	root		inner join, inner:Selection, outer key:expression__issues.t1.id, inner key:expression__issues.t2.order_id, equal cond:eq(expression__issues.t1.id, expression__issues.t2.order_id)
+└─IndexJoin	0.03	root		inner join, inner:IndexLookUp, outer key:expression__issues.t1.id, inner key:expression__issues.t2.order_id, equal cond:eq(expression__issues.t1.id, expression__issues.t2.order_id)
   ├─TableReader(Build)	0.02	root		data:Selection
   │ └─Selection	0.02	cop[tikv]		eq(cast(expression__issues.t1.org_id, double BINARY), 1), eq(expression__issues.t1.ns, "a"), in(expression__issues.t1.status, 2, 6, 10)
   │   └─TableFullScan	10000.00	cop[tikv]	table:t1	keep order:false, stats:pseudo
-  └─Selection(Probe)	0.03	root		eq(timestampdiff("MONTH", expression__issues.t2.begin_time, 2020-05-06), 0)
-    └─IndexLookUp	0.04	root		
-      ├─IndexRangeScan(Build)	0.04	cop[tikv]	table:t2, index:idx_oid(order_id)	range: decided by [eq(expression__issues.t2.order_id, expression__issues.t1.id)], keep order:false, stats:pseudo
-      └─TableRowIDScan(Probe)	0.04	cop[tikv]	table:t2	keep order:false, stats:pseudo
+  └─IndexLookUp(Probe)	0.03	root		
+    ├─IndexRangeScan(Build)	0.04	cop[tikv]	table:t2, index:idx_oid(order_id)	range: decided by [eq(expression__issues.t2.order_id, expression__issues.t1.id)], keep order:false, stats:pseudo
+    └─Selection(Probe)	0.03	cop[tikv]		eq(timestampdiff("MONTH", expression__issues.t2.begin_time, 2020-05-06), 0)
+      └─TableRowIDScan	0.04	cop[tikv]	table:t2	keep order:false, stats:pseudo
 SELECT /*+ INL_MERGE_JOIN(t1,t2) */ COUNT(*) FROM  t1 LEFT JOIN t2 ON t1.id = t2.order_id WHERE t1.ns = 'a' AND t1.org_id IN (1) AND t1.status IN (2,6,10) AND timestampdiff(month, t2.begin_time, date'2020-05-06') = 0;
 COUNT(*)
 1