diff --git a/os/gcfg/gcfg.go b/os/gcfg/gcfg.go
index b994a31cf..1256a6fa3 100644
--- a/os/gcfg/gcfg.go
+++ b/os/gcfg/gcfg.go
@@ -40,7 +40,7 @@ type Config struct {
 }
 
 var (
-	supportedFileTypes = []string{"toml", "yaml", "json", "ini", "xml"}
+	supportedFileTypes = []string{"toml", "yaml", "yml", "json", "ini", "xml"}
 	resourceTryFiles   = []string{"", "/", "config/", "config", "/config", "/config/"}
 )
 
diff --git a/os/gcfg/gcfg_instance.go b/os/gcfg/gcfg_instance.go
index 84999034f..9eeb07905 100644
--- a/os/gcfg/gcfg_instance.go
+++ b/os/gcfg/gcfg_instance.go
@@ -32,10 +32,15 @@ func Instance(name ...string) *Config {
 	}
 	return instances.GetOrSetFuncLock(key, func() interface{} {
 		c := New()
-		for _, fileType := range supportedFileTypes {
-			if file := fmt.Sprintf(`%s.%s`, key, fileType); c.Available(file) {
-				c.SetFileName(file)
-				break
+		// If it's not using default configuration or its configuration file is not available,
+		// it searches the possible configuration file according to the name and all supported
+		// file types.
+		if key != DefaultName || !c.Available() {
+			for _, fileType := range supportedFileTypes {
+				if file := fmt.Sprintf(`%s.%s`, key, fileType); c.Available(file) {
+					c.SetFileName(file)
+					break
+				}
 			}
 		}
 		return c
diff --git a/os/gcfg/gcfg_z_unit_instance_test.go b/os/gcfg/gcfg_z_unit_instance_test.go
index 9043bf434..2cc5e3ab1 100644
--- a/os/gcfg/gcfg_z_unit_instance_test.go
+++ b/os/gcfg/gcfg_z_unit_instance_test.go
@@ -78,7 +78,6 @@ v4 = "1.234"
 			"cache": "127.0.0.1:6379,1",
 		})
 		t.AssertEQ(c.FilePath(), gfile.Pwd()+gfile.Separator+path)
-
 	})
 }
 
@@ -89,7 +88,7 @@ func Test_Instance_AutoLocateConfigFile(t *testing.T) {
 	// Automatically locate the configuration file with supported file extensions.
 	gtest.C(t, func(t *gtest.T) {
 		pwd := gfile.Pwd()
-		gfile.Chdir(gdebug.TestDataPath())
+		t.AssertNil(gfile.Chdir(gdebug.TestDataPath()))
 		defer gfile.Chdir(pwd)
 		t.Assert(Instance("c1") != nil, true)
 		t.Assert(Instance("c1").Get("my-config"), "1")
@@ -98,10 +97,23 @@ func Test_Instance_AutoLocateConfigFile(t *testing.T) {
 	// Automatically locate the configuration file with supported file extensions.
 	gtest.C(t, func(t *gtest.T) {
 		pwd := gfile.Pwd()
-		gfile.Chdir(gdebug.TestDataPath("folder1"))
+		t.AssertNil(gfile.Chdir(gdebug.TestDataPath("folder1")))
 		defer gfile.Chdir(pwd)
 		t.Assert(Instance("c2").Get("my-config"), 2)
 	})
+	// Default configuration file.
+	gtest.C(t, func(t *gtest.T) {
+		instances.Clear()
+		pwd := gfile.Pwd()
+		t.AssertNil(gfile.Chdir(gdebug.TestDataPath("default")))
+		defer gfile.Chdir(pwd)
+		t.Assert(Instance().Get("my-config"), 1)
+
+		instances.Clear()
+		t.AssertNil(genv.Set("GF_GCFG_FILE", "config.json"))
+		defer genv.Set("GF_GCFG_FILE", "")
+		t.Assert(Instance().Get("my-config"), 2)
+	})
 }
 
 func Test_Instance_EnvPath(t *testing.T) {
diff --git a/os/gcfg/testdata/default/config.json b/os/gcfg/testdata/default/config.json
new file mode 100644
index 000000000..ea5047901
--- /dev/null
+++ b/os/gcfg/testdata/default/config.json
@@ -0,0 +1 @@
+{"my-config": 2}
\ No newline at end of file
diff --git a/os/gcfg/testdata/default/config.toml b/os/gcfg/testdata/default/config.toml
new file mode 100644
index 000000000..ec4ea12a8
--- /dev/null
+++ b/os/gcfg/testdata/default/config.toml
@@ -0,0 +1 @@
+my-config = "1"
\ No newline at end of file