diff --git a/README.md b/README.md
index fa72efdb..d069e87f 100644
--- a/README.md
+++ b/README.md
@@ -92,8 +92,8 @@ allow-lan: false
 # "[aaaa::a8aa:ff:fe09:57d8]": bind a single IPv6 address
 # bind-address: "*"
 
-# Rule / Global / Direct (default is Rule)
-mode: Rule
+# rule / global / direct (default is rule)
+mode: rule
 
 # set log level to stdout (default is info)
 # info / warning / error / debug / silent
diff --git a/tunnel/mode.go b/tunnel/mode.go
index 655c9f57..6e07a060 100644
--- a/tunnel/mode.go
+++ b/tunnel/mode.go
@@ -3,6 +3,7 @@ package tunnel
 import (
 	"encoding/json"
 	"errors"
+	"strings"
 )
 
 type TunnelMode int
@@ -26,7 +27,7 @@ const (
 func (m *TunnelMode) UnmarshalJSON(data []byte) error {
 	var tp string
 	json.Unmarshal(data, &tp)
-	mode, exist := ModeMapping[tp]
+	mode, exist := ModeMapping[strings.ToLower(tp)]
 	if !exist {
 		return errors.New("invalid mode")
 	}
@@ -38,7 +39,7 @@ func (m *TunnelMode) UnmarshalJSON(data []byte) error {
 func (m *TunnelMode) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	var tp string
 	unmarshal(&tp)
-	mode, exist := ModeMapping[tp]
+	mode, exist := ModeMapping[strings.ToLower(tp)]
 	if !exist {
 		return errors.New("invalid mode")
 	}
@@ -59,11 +60,11 @@ func (m TunnelMode) MarshalYAML() (interface{}, error) {
 func (m TunnelMode) String() string {
 	switch m {
 	case Global:
-		return "Global"
+		return "global"
 	case Rule:
-		return "Rule"
+		return "rule"
 	case Direct:
-		return "Direct"
+		return "direct"
 	default:
 		return "Unknown"
 	}