diff --git a/env.go b/env.go
index f5348ef..b5712b7 100644
--- a/env.go
+++ b/env.go
@@ -12,17 +12,37 @@ import (
 var (
 	defaultSep = "_"
 )
+var env *Env
+type Env struct {
+	ignorePrefix bool
+}
+
+func init() {
+	env = &Env{false}
+}
 
 func upper(v string) string {
 	return strings.ToUpper(v)
 }
 
+func IgnorePrefix() {
+	env.ignorePrefix = true
+}
+
 func Fill(v interface{}) error {
-	if reflect.ValueOf(v).Kind() != reflect.Ptr {
+	return env.Fill(v)
+}
+
+func (e *Env)Fill(v interface{}) error {
+	ind := reflect.Indirect(reflect.ValueOf(v))
+	if reflect.ValueOf(v).Kind() != reflect.Ptr || ind.Kind() != reflect.Struct{
 		return fmt.Errorf("only the pointer to a struct is supported")
 	}
-	ind := reflect.Indirect(reflect.ValueOf(v))
+
 	prefix := upper(ind.Type().Name())
+	if e.ignorePrefix {
+		prefix = ""
+	}
 	err := fill(prefix, ind)
 	if err != nil {
 		return err
@@ -30,11 +50,14 @@ func Fill(v interface{}) error {
 	return nil
 }
 
-func combine(p, n string, v string, ok bool) string {
+func combine(p, n string, sep string, ok bool) string {
+	if p == "" {
+		return n
+	}
 	if !ok {
 		return p + defaultSep + n
 	}
-	return p + v + n
+	return p + sep + n
 }
 
 func parseBool(v string) (bool, error) {
@@ -71,7 +94,6 @@ func fill(pf string, ind reflect.Value) error {
 }
 
 func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
-	//log.Print("parse:", prefix, f.String(), f.Type().String(), f.Kind().String())
 	df := sf.Tag.Get("default")
 	isRequire, err := parseBool(sf.Tag.Get("require"))
 	if err != nil {
@@ -93,51 +115,51 @@ func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
 	case reflect.Int:
 		iv, err := strconv.ParseInt(ev, 10, 32)
 		if err != nil {
-			return err
+			return fmt.Errorf("%s:%s", prefix, err)
 		}
 		f.SetInt(iv)
 	case reflect.Int64:
 		if f.Type().String() == "time.Duration" {
 			t, err := time.ParseDuration(ev)
 			if err != nil {
-				return err
+				return fmt.Errorf("%s:%s", prefix, err)
 			}
 			f.Set(reflect.ValueOf(t))
 		} else {
 			iv, err := strconv.ParseInt(ev, 10, 64)
 			if err != nil {
-				return err
+				return fmt.Errorf("%s:%s", prefix, err)
 			}
 			f.SetInt(iv)
 		}
 	case reflect.Uint:
 		uiv, err := strconv.ParseUint(ev, 10, 32)
 		if err != nil {
-			return err
+			return fmt.Errorf("%s:%s", prefix, err)
 		}
 		f.SetUint(uiv)
 	case reflect.Uint64:
 		uiv, err := strconv.ParseUint(ev, 10, 64)
 		if err != nil {
-			return err
+			return fmt.Errorf("%s:%s", prefix, err)
 		}
 		f.SetUint(uiv)
 	case reflect.Float32:
 		f32, err := strconv.ParseFloat(ev, 32)
 		if err != nil {
-			return err
+			return fmt.Errorf("%s:%s", prefix, err)
 		}
 		f.SetFloat(f32)
 	case reflect.Float64:
 		f64, err := strconv.ParseFloat(ev, 64)
 		if err != nil {
-			return err
+			return fmt.Errorf("%s:%s", prefix, err)
 		}
 		f.SetFloat(f64)
 	case reflect.Bool:
 		b, err := parseBool(ev)
 		if err != nil {
-			return err
+			return fmt.Errorf("%s:%s", prefix, err)
 		}
 		f.SetBool(b)
 	case reflect.Slice:
@@ -155,7 +177,7 @@ func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
 			for i, v := range vals {
 				val, err := strconv.ParseInt(v, 10, 32)
 				if err != nil {
-					return err
+					return fmt.Errorf("%s:%s", prefix, err)
 				}
 				t[i] = int(val)
 			}
@@ -164,7 +186,7 @@ func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
 			for i, v := range vals {
 				val, err := strconv.ParseInt(v, 10, 64)
 				if err != nil {
-					return err
+					return fmt.Errorf("%s:%s", prefix, err)
 				}
 				t[i] = val
 			}
@@ -173,7 +195,7 @@ func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
 			for i, v := range vals {
 				val, err := strconv.ParseUint(v, 10, 32)
 				if err != nil {
-					return err
+					return fmt.Errorf("%s:%s", prefix, err)
 				}
 				t[i] = uint(val)
 			}
@@ -182,7 +204,7 @@ func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
 			for i, v := range vals {
 				val, err := strconv.ParseUint(v, 10, 64)
 				if err != nil {
-					return err
+					return fmt.Errorf("%s:%s", prefix, err)
 				}
 				t[i] = val
 			}
@@ -191,7 +213,7 @@ func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
 			for i, v := range vals {
 				val, err := strconv.ParseFloat(v, 32)
 				if err != nil {
-					return err
+					return fmt.Errorf("%s:%s", prefix, err)
 				}
 				t[i] = float32(val)
 			}
@@ -200,7 +222,7 @@ func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
 			for i, v := range vals {
 				val, err := strconv.ParseFloat(v, 64)
 				if err != nil {
-					return err
+					return fmt.Errorf("%s:%s", prefix, err)
 				}
 				t[i] = val
 			}
@@ -209,7 +231,7 @@ func parse(prefix string, f reflect.Value, sf reflect.StructField) error {
 			for i, v := range vals {
 				val, err := parseBool(v)
 				if err != nil {
-					return err
+					return fmt.Errorf("%s:%s", prefix, err)
 				}
 				t[i] = val
 			}
diff --git a/env_test.go b/env_test.go
new file mode 100644
index 0000000..08022af
--- /dev/null
+++ b/env_test.go
@@ -0,0 +1,103 @@
+package env
+
+import (
+	"testing"
+	"os"
+	"time"
+	"github.com/stretchr/testify/assert"
+)
+type config struct {
+	App     string
+	Port    int      `default:"8000"`
+	IsDebug  bool     `env:"DEBUG"`
+	Hosts   []string `slice_sep:","`
+	Timeout time.Duration
+
+	Redis struct {
+		Version string `sep:""` // no sep between `CONFIG` and `REDIS`
+		Host    string
+		Port    int
+	}
+
+	MySQL struct {
+		Version string `default:"5.7"`
+		Host    string
+		Port    int
+	}
+}
+func TestGeneralEnv(t *testing.T) {
+	os.Setenv("CONFIG_APP", "ENV APP")
+	// os.Setenv("CONFIG_PORT", "default") // default value
+	os.Setenv("CONFIG_DEBUG", "1")
+	os.Setenv("CONFIG_HOSTS", "192.168.0.1,127.0.0.1")
+	os.Setenv("CONFIG_TIMEOUT", "5s")
+
+	os.Setenv("CONFIG_REDISVERSION", "3.2")
+	os.Setenv("CONFIG_REDIS_HOST", "rdb")
+	os.Setenv("CONFIG_REDIS_PORT", "6379")
+
+	os.Setenv("CONFIG_MYSQL_HOST", "mysqldb")
+	os.Setenv("CONFIG_MYSQL_PORT", "3306")
+
+	defer os.Clearenv()
+
+	cfg := new(config)
+	err := Fill(cfg)
+	if err != nil {
+		t.Error(err)
+	}
+
+	assert := assert.New(t)
+
+	assert.Equal(cfg.App, "ENV APP")
+	assert.Equal(cfg.Port, 8000)
+	assert.Equal(cfg.IsDebug, true)
+	assert.Equal(cfg.Hosts, []string{"192.168.0.1", "127.0.0.1"})
+	assert.Equal(cfg.Timeout, 5*time.Second)
+	assert.Equal(cfg.Redis.Version, "3.2")
+	assert.Equal(cfg.Redis.Host, "rdb")
+	assert.Equal(cfg.MySQL.Version, "5.7")
+	assert.Equal(cfg.MySQL.Host, "mysqldb")
+	assert.Equal(cfg.MySQL.Port, 3306)
+
+}
+
+
+
+func TestNoPrefixEnv(t *testing.T) {
+	os.Setenv("APP", "ENV_APP")
+	// os.Setenv("PORT", "default") // default value
+	os.Setenv("DEBUG", "1")
+	os.Setenv("HOSTS", "192.168.1.1,127.0.0.1")
+	os.Setenv("TIMEOUT", "5s")
+
+	os.Setenv("REDISVERSION", "3.2")
+	os.Setenv("REDIS_HOST", "rdb")
+	os.Setenv("REDIS_PORT", "6379")
+
+	os.Setenv("MYSQL_HOST", "mysqldb")
+	os.Setenv("MYSQL_PORT", "3306")
+
+	defer os.Clearenv()
+
+	cfg := new(config)
+	IgnorePrefix()
+	err := Fill(cfg)
+	if err != nil {
+		t.Error(err)
+	}
+
+	assert := assert.New(t)
+
+	assert.Equal(cfg.App, "ENV_APP")
+	assert.Equal(cfg.Port, 8000)
+	assert.Equal(cfg.IsDebug, true)
+	assert.Equal(cfg.Hosts, []string{"192.168.1.1", "127.0.0.1"})
+	assert.Equal(cfg.Timeout, 5*time.Second)
+	assert.Equal(cfg.Redis.Version, "3.2")
+	assert.Equal(cfg.Redis.Host, "rdb")
+	assert.Equal(cfg.MySQL.Version, "5.7")
+	assert.Equal(cfg.MySQL.Host, "mysqldb")
+	assert.Equal(cfg.MySQL.Port, 3306)
+
+}
\ No newline at end of file