diff --git a/feeluown/config.py b/feeluown/config.py
index 2bcfe9167..067d6e370 100644
--- a/feeluown/config.py
+++ b/feeluown/config.py
@@ -1,3 +1,4 @@
+from typing import Optional
 import logging
 import warnings
 from collections import namedtuple
@@ -15,19 +16,33 @@ class Config:
     用户可以在 rc 文件中配置各个选项的值
     """
 
-    def __init__(self):
+    def __init__(self, name: str = 'config', parent: Optional['Config'] = None):
+        object.__setattr__(self, '_name', name)
+        object.__setattr__(self, '_parent', parent)
         object.__setattr__(self, '_fields', {})
+        object.__setattr__(self, '_undeclared_fields', {})
 
     def __getattr__(self, name):
         # tips: 这里不能用 getattr 来获取值, 否则会死循环
-        if name == '_fields':
-            return object.__getattribute__(self, '_fields')
+        if name in ('_fields', '_parent', '_name', '_undeclared_fields'):
+            return object.__getattribute__(self, name)
         if name in self._fields:
             try:
-                object.__getattribute__(self, name)
+                return object.__getattribute__(self, name)
             except AttributeError:
                 return self._fields[name].default
-        return object.__getattribute__(self, name)
+        elif name in self._undeclared_fields:
+            return self._undeclared_fields[name]
+
+        # Requirement:
+        #   User may define config like
+        #       app.plugin.X = Y
+        #   When 'plugin' is not installed, such config should not raise an error.
+        # To achieve this, return a subconfig when accessing an undeclared key.
+        logger.warning(f'Undeclared subconfig: {self.fullname}.{name}')
+        tmpconfig = Config(name=name, parent=self)
+        self._undeclared_fields[name] = tmpconfig
+        return tmpconfig
 
     def __setattr__(self, name, value):
         if name in self._fields:
@@ -38,7 +53,13 @@ def __setattr__(self, name, value):
             # TODO: 校验值类型
             object.__setattr__(self, name, value)
         else:
-            logger.warning('Assign to an undeclared config key.')
+            logger.warning(f'Assign to an undeclared config key: {self.fullname}.{name}')
+
+    @property
+    def fullname(self) -> str:
+        if self._parent is None:
+            return self._name
+        return f'{self._parent.fullname}.{self._name}'
 
     def deffield(self, name, type_=None, default=None, desc='', warn=None):
         """Define a configuration field
diff --git a/feeluown/plugin.py b/feeluown/plugin.py
index 19ef1301e..7e8df443a 100644
--- a/feeluown/plugin.py
+++ b/feeluown/plugin.py
@@ -91,7 +91,7 @@ def init_config(self, config: Config):
 
         .. versionadded: 3.7.15
         """
-        myconfig = Config()
+        myconfig = Config(name=self.name, parent=config)
 
         names = [self.name]
         # Currently, plugin name looks like fuo_xxx and xxx is the real name.
diff --git a/tests/test_config.py b/tests/test_config.py
index 0b8b62a7f..f0a5410b1 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -17,10 +17,14 @@ def test_config_set_known_field(config):
 
 
 def test_config_set_unknown_field(config):
-    """Set unknown field should cause no effects"""
+    """
+    Set unknown field should cause no effects.
+    Access unknown field should return a Config object.
+    """
     config.hey = 0
-    with pytest.raises(AttributeError):
-        config.hey
+    assert isinstance(config.hey, Config)
+    config.plugin.X = 0  # should not raise error
+    assert isinstance(config.plugin.X, Config)
 
 
 def test_config_set_subconfig(config):