diff --git a/util/logutil/log.go b/util/logutil/log.go
index 582ef36f46cf5..66bee73e69fb3 100644
--- a/util/logutil/log.go
+++ b/util/logutil/log.go
@@ -42,8 +42,6 @@ const (
 	DefaultRecordPlanInSlowLog = 1
 	// DefaultTiDBEnableSlowLog enables TiDB to log slow queries.
 	DefaultTiDBEnableSlowLog = true
-	// GRPCLogDebugVerbosity enables max verbosity when debugging grpc code.
-	GRPCLogDebugVerbosity = 99
 )
 
 // EmptyFileLogConfig is an empty FileLogConfig.
@@ -106,20 +104,42 @@ func InitLogger(cfg *LogConfig) error {
 	log.ReplaceGlobals(gl, props)
 
 	// init dedicated logger for slow query log
-	SlowQueryLogger, err = newSlowQueryLogger(cfg)
+	SlowQueryLogger, _, err = newSlowQueryLogger(cfg)
 	if err != nil {
 		return errors.Trace(err)
 	}
 
-	// init logger for grpc debugging
+	_, _, err = initGRPCLogger(cfg)
+	if err != nil {
+		return errors.Trace(err)
+	}
+
+	return nil
+}
+
+func initGRPCLogger(cfg *LogConfig) (*zap.Logger, *log.ZapProperties, error) {
+	// Copy Config struct by assignment.
+	config := cfg.Config
+	var l *zap.Logger
+	var err error
+	var prop *log.ZapProperties
 	if len(os.Getenv("GRPC_DEBUG")) > 0 {
-		// more information for verbosity: https://github.com/google/glog#verbose-logging
-		gzap.ReplaceGrpcLoggerV2WithVerbosity(gl, GRPCLogDebugVerbosity)
+		config.Level = "debug"
+		l, prop, err = log.InitLogger(&config, zap.AddStacktrace(zapcore.FatalLevel))
+		if err != nil {
+			return nil, nil, errors.Trace(err)
+		}
+		gzap.ReplaceGrpcLoggerV2WithVerbosity(l, 999)
 	} else {
-		gzap.ReplaceGrpcLoggerV2(gl)
+		config.Level = "error"
+		l, prop, err = log.InitLogger(&config, zap.AddStacktrace(zapcore.FatalLevel))
+		if err != nil {
+			return nil, nil, errors.Trace(err)
+		}
+		gzap.ReplaceGrpcLoggerV2(l)
 	}
 
-	return nil
+	return l, prop, nil
 }
 
 // SetLevel sets the zap logger's level.
diff --git a/util/logutil/log_test.go b/util/logutil/log_test.go
index a78efa657f247..4c5232c50cd1f 100644
--- a/util/logutil/log_test.go
+++ b/util/logutil/log_test.go
@@ -97,3 +97,28 @@ func TestSetLevel(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, zap.DebugLevel, log.GetLevel())
 }
+
+func TestGrpcLoggerCreation(t *testing.T) {
+	level := "info"
+	conf := NewLogConfig(level, DefaultLogFormat, "", EmptyFileLogConfig, false)
+	_, p, err := initGRPCLogger(conf)
+	// assert after init grpc logger, the original conf is not changed
+	require.Equal(t, conf.Level, level)
+	require.Nil(t, err)
+	require.Equal(t, p.Level.Level(), zap.ErrorLevel)
+	os.Setenv("GRPC_DEBUG", "1")
+	defer os.Unsetenv("GRPC_DEBUG")
+	_, newP, err := initGRPCLogger(conf)
+	require.Nil(t, err)
+	require.Equal(t, newP.Level.Level(), zap.DebugLevel)
+}
+
+func TestSlowQueryLoggerCreation(t *testing.T) {
+	level := "warn"
+	conf := NewLogConfig(level, DefaultLogFormat, "", EmptyFileLogConfig, false)
+	_, prop, err := newSlowQueryLogger(conf)
+	// assert after init slow query logger, the original conf is not changed
+	require.Equal(t, conf.Level, level)
+	require.Nil(t, err)
+	require.Equal(t, prop.Level.String(), conf.Level)
+}
diff --git a/util/logutil/slow_query_logger.go b/util/logutil/slow_query_logger.go
index 3910b6ecd1192..433fd5746eca7 100644
--- a/util/logutil/slow_query_logger.go
+++ b/util/logutil/slow_query_logger.go
@@ -13,11 +13,11 @@ import (
 
 var _pool = buffer.NewPool()
 
-func newSlowQueryLogger(cfg *LogConfig) (*zap.Logger, error) {
+func newSlowQueryLogger(cfg *LogConfig) (*zap.Logger, *log.ZapProperties, error) {
 
-	// reuse global config and override slow query log file
+	// copy global config and override slow query log file
 	// if slow query log filename is empty, slow query log will behave the same as global log
-	sqConfig := &cfg.Config
+	sqConfig := cfg.Config
 	if len(cfg.SlowQueryFile) != 0 {
 		sqConfig.File = log.FileLogConfig{
 			MaxSize:  cfg.File.MaxSize,
@@ -26,17 +26,19 @@ func newSlowQueryLogger(cfg *LogConfig) (*zap.Logger, error) {
 	}
 
 	// create the slow query logger
-	sqLogger, prop, err := log.InitLogger(sqConfig)
+	sqLogger, prop, err := log.InitLogger(&sqConfig)
 	if err != nil {
-		return nil, errors.Trace(err)
+		return nil, nil, errors.Trace(err)
 	}
 
 	// replace 2018-12-19-unified-log-format text encoder with slow log encoder
+	newCore := log.NewTextCore(&slowLogEncoder{}, prop.Syncer, prop.Level)
 	sqLogger = sqLogger.WithOptions(zap.WrapCore(func(core zapcore.Core) zapcore.Core {
-		return log.NewTextCore(&slowLogEncoder{}, prop.Syncer, prop.Level)
+		return newCore
 	}))
+	prop.Core = newCore
 
-	return sqLogger, nil
+	return sqLogger, prop, nil
 }
 
 type slowLogEncoder struct{}