diff --git a/config/config.go b/config/config.go
index d6babffa84bb1..4df542b8483c7 100644
--- a/config/config.go
+++ b/config/config.go
@@ -127,11 +127,12 @@ type Security struct {
 // This is needed only because logging hasn't been set up at the time we parse the config file.
 // This should all be ripped out once strict config checking is made the default behavior.
 type ErrConfigValidationFailed struct {
-	err string
+	confFile       string
+	UndecodedItems []string
 }
 
 func (e *ErrConfigValidationFailed) Error() string {
-	return e.err
+	return fmt.Sprintf("config file %s contained unknown configuration options: %s", e.confFile, strings.Join(e.UndecodedItems, ", "))
 }
 
 // ToTLSConfig generates tls's config based on security section of the config.
@@ -538,7 +539,7 @@ func (c *Config) Load(confFile string) error {
 		for _, item := range undecoded {
 			undecodedItems = append(undecodedItems, item.String())
 		}
-		err = &ErrConfigValidationFailed{fmt.Sprintf("config file %s contained unknown configuration options: %s", confFile, strings.Join(undecodedItems, ", "))}
+		err = &ErrConfigValidationFailed{confFile, undecodedItems}
 	}
 
 	return err
diff --git a/tidb-server/main.go b/tidb-server/main.go
index 3396e42fe568b..19f889580d6d5 100644
--- a/tidb-server/main.go
+++ b/tidb-server/main.go
@@ -305,6 +305,20 @@ func flagBoolean(name string, defaultVal bool, usage string) *bool {
 	return flag.Bool(name, defaultVal, usage)
 }
 
+var deprecatedConfig = map[string]struct{}{
+	"pessimistic-txn.ttl": {},
+	"log.rotate":          {},
+}
+
+func isDeprecatedConfigItem(items []string) bool {
+	for _, item := range items {
+		if _, ok := deprecatedConfig[item]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
 func loadConfig() string {
 	cfg = config.GetGlobalConfig()
 	if *configPath != "" {
@@ -312,13 +326,24 @@ func loadConfig() string {
 		config.SetConfReloader(*configPath, reloadConfig, hotReloadConfigItems...)
 
 		err := cfg.Load(*configPath)
-		// This block is to accommodate an interim situation where strict config checking
-		// is not the default behavior of TiDB. The warning message must be deferred until
-		// logging has been set up. After strict config checking is the default behavior,
-		// This should all be removed.
-		if _, ok := err.(*config.ErrConfigValidationFailed); ok && !*configCheck && !*configStrict {
-			return err.Error()
+		if err == nil {
+			return ""
+		}
+
+		// Unused config item erro turns to warnings.
+		if tmp, ok := err.(*config.ErrConfigValidationFailed); ok {
+			if isDeprecatedConfigItem(tmp.UndecodedItems) {
+				return err.Error()
+			}
+			// This block is to accommodate an interim situation where strict config checking
+			// is not the default behavior of TiDB. The warning message must be deferred until
+			// logging has been set up. After strict config checking is the default behavior,
+			// This should all be removed.
+			if !*configCheck && !*configStrict {
+				return err.Error()
+			}
 		}
+
 		terror.MustNil(err)
 	} else {
 		// configCheck should have the config file specified.