diff --git a/pkg/task/common_test.go b/pkg/task/common_test.go
index 6c4869809..b28809d59 100644
--- a/pkg/task/common_test.go
+++ b/pkg/task/common_test.go
@@ -5,6 +5,8 @@ package task
 import (
 	"fmt"
 
+	"github.com/pingcap/tidb/config"
+
 	. "github.com/pingcap/check"
 	"github.com/spf13/pflag"
 )
@@ -37,3 +39,11 @@ func (*testCommonSuite) TestUrlNoQuery(c *C) {
 	c.Assert(field.Key, Equals, flagStorage)
 	c.Assert(field.Interface.(fmt.Stringer).String(), Equals, "s3://some/what")
 }
+
+func (s *testCommonSuite) TestTiDBConfigUnchanged(c *C) {
+	cfg := config.GetGlobalConfig()
+	restoreConfig := enableTiDBConfig()
+	c.Assert(cfg, Not(DeepEquals), config.GetGlobalConfig())
+	restoreConfig()
+	c.Assert(cfg, DeepEquals, config.GetGlobalConfig())
+}
diff --git a/pkg/task/restore.go b/pkg/task/restore.go
index 3cb5e867b..0e57f7a68 100644
--- a/pkg/task/restore.go
+++ b/pkg/task/restore.go
@@ -154,7 +154,8 @@ func RunRestore(c context.Context, g glue.Glue, cmdName string, cfg *RestoreConf
 	ddlJobs := restore.FilterDDLJobs(client.GetDDLJobs(), tables)
 
 	// pre-set TiDB config for restore
-	enableTiDBConfig()
+	restoreDBConfig := enableTiDBConfig()
+	defer restoreDBConfig()
 
 	// execute DDL first
 	err = client.ExecDDLs(ddlJobs)
@@ -413,21 +414,23 @@ func RunRestoreTiflashReplica(c context.Context, g glue.Glue, cmdName string, cf
 	return nil
 }
 
-func enableTiDBConfig() {
-	// set max-index-length before execute DDLs and create tables
-	// we set this value to max(3072*4), otherwise we might not restore table
-	// when upstream and downstream both set this value greater than default(3072)
-	conf := config.GetGlobalConfig()
-	conf.MaxIndexLength = config.DefMaxOfMaxIndexLength
-	log.Warn("set max-index-length to max(3072*4) to skip check index length in DDL")
-
-	// we need set this to true, since all create table DDLs will create with tableInfo
-	// and we can handle alter drop pk/add pk DDLs with no impact
-	conf.AlterPrimaryKey = true
-
-	conf.Experimental.AllowsExpressionIndex = true
+// enableTiDBConfig tweaks some of configs of TiDB to make the restore progress go well.
+// return a function that could restore the config to origin.
+func enableTiDBConfig() func() {
+	restoreConfig := config.RestoreFunc()
+	config.UpdateGlobal(func(conf *config.Config) {
+		// set max-index-length before execute DDLs and create tables
+		// we set this value to max(3072*4), otherwise we might not restore table
+		// when upstream and downstream both set this value greater than default(3072)
+		conf.MaxIndexLength = config.DefMaxOfMaxIndexLength
+		log.Warn("set max-index-length to max(3072*4) to skip check index length in DDL")
+
+		// we need set this to true, since all create table DDLs will create with tableInfo
+		// and we can handle alter drop pk/add pk DDLs with no impact
+		conf.AlterPrimaryKey = true
+	})
 
-	config.StoreGlobalConfig(conf)
+	return restoreConfig
 }
 
 // restoreTableStream blocks current goroutine and restore a stream of tables,
diff --git a/tests/br_db/run.sh b/tests/br_db/run.sh
index 4ea4a2d39..de515bd06 100755
--- a/tests/br_db/run.sh
+++ b/tests/br_db/run.sh
@@ -16,6 +16,7 @@
 set -eu
 DB="$TEST_NAME"
 
+old_conf=$(run_sql "show config where name = 'alter-primary-key'")
 run_sql "CREATE DATABASE $DB;"
 
 run_sql "CREATE TABLE $DB.usertable1 ( \
@@ -34,7 +35,6 @@ run_sql "CREATE TABLE $DB.usertable2 ( \
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;"
 
 run_sql "INSERT INTO $DB.usertable2 VALUES (\"c\", \"d\");"
-
 # backup db
 echo "backup start..."
 run_br --pd $PD_ADDR backup db --db "$DB" -s "local://$TEST_DIR/$DB" --ratelimit 5 --concurrency 4
@@ -56,4 +56,7 @@ echo "testing DDL query..."
 curl 127.0.0.1:10080/ddl/history | grep -E '/\*from\(br\)\*/CREATE TABLE'
 curl 127.0.0.1:10080/ddl/history | grep -E '/\*from\(br\)\*/CREATE DATABASE'
 
+# test whether we have changed the cluster config.
+test "$old_conf" = "$(run_sql "show config where name = 'alter-primary-key'")"
+
 run_sql "DROP DATABASE $DB;"
diff --git a/tests/br_full/run.sh b/tests/br_full/run.sh
index 6100c980d..6fe00a17d 100755
--- a/tests/br_full/run.sh
+++ b/tests/br_full/run.sh
@@ -17,6 +17,7 @@ set -eu
 DB="$TEST_NAME"
 TABLE="usertable"
 DB_COUNT=3
+old_conf=$(run_sql "show config where name = 'alter-primary-key'")
 
 for i in $(seq $DB_COUNT); do
     run_sql "CREATE DATABASE $DB${i};"
@@ -71,6 +72,9 @@ for ct in lz4 zstd; do
   fi
 done
 
+# test whether we have changed the cluster config.
+test "$old_conf" = "$(run_sql "show config where name = 'alter-primary-key'")"
+
 for i in $(seq $DB_COUNT); do
     run_sql "DROP DATABASE $DB${i};"
 done