diff --git a/dm/pkg/schema/tracker.go b/dm/pkg/schema/tracker.go
index de783f4caef..86635759491 100644
--- a/dm/pkg/schema/tracker.go
+++ b/dm/pkg/schema/tracker.go
@@ -117,6 +117,8 @@ func NewTracker(ctx context.Context, task string, sessionCfg map[string]string,
 		// bypass wait time of https://github.com/pingcap/tidb/pull/20550
 		conf.TiKVClient.AsyncCommit.SafeWindow = 0
 		conf.TiKVClient.AsyncCommit.AllowedClockDrift = 0
+		// bypass "Specified key was too long"
+		conf.MaxIndexLength = 1<<32 - 1
 	})
 
 	if len(sessionCfg) == 0 {
diff --git a/dm/pkg/schema/tracker_test.go b/dm/pkg/schema/tracker_test.go
index a3c6910b029..c8f7d0a2f94 100644
--- a/dm/pkg/schema/tracker_test.go
+++ b/dm/pkg/schema/tracker_test.go
@@ -958,7 +958,7 @@ func (s *trackerSuite) TestVarchar20000(c *C) {
 
 	mock.ExpectQuery("SHOW CREATE TABLE " + tableID).WillReturnRows(
 		sqlmock.NewRows([]string{"Table", "Create Table"}).
-			AddRow("test", "create table t(c varchar(20000)) charset=utf8"))
+			AddRow("test", "create table t(c varchar(20000), key(c(20000))) charset=utf8"))
 	_, err = tracker.GetDownStreamTableInfo(tcontext.Background(), tableID, oriTi)
 	c.Assert(err, IsNil)
 	_, ok := tracker.dsTracker.tableInfos[tableID]