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diff --git a/doc/nerv_class.md b/doc/nerv_class.md
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--- a/doc/nerv_class.md
+++ b/doc/nerv_class.md
@@ -1,3 +1,36 @@
 #The Nerv OOP#
 Part of the [Nerv](../README.md) toolkit.
 ##Methods##
+* __metatable mt, metatable mpt = nerv.class(string tname, string parenttname)__  
+This method is used to create a class by the name `tname`, which inherits `parenttname` in __Nerv__, then you create a new instance of this class by calling `obj=tname(...)`. The  `tname.__init(...)` method(if defined) will be called in the constructing. The metatable of the class and its parent class will be returned.
+
+##Examples##
+* This example implements a simple `nerv.Counter` class which is inherited by `nerv.BetterCounter`.  
+
+```
+do
+    nerv.class("nerv.Counter")
+    function nerv.Counter:__init(c)
+        if (c) then
+            self.c = c
+        else
+            self.c = 0
+        end
+    end
+end
+do
+    local mt, mpt = nerv.class("nerv.BetterCounter", "nerv.Counter")
+    function nerv.BetterCounter:__init(c, bc)
+        mpt.__init(self, c)
+        if (bc) then
+            self.bc = bc
+        else
+            self.bc = 0
+        end
+    end
+end
+c1 = nerv.Counter(1)
+print(c1.c)
+bc1 = nerv.BetterCounter(1, 1)
+print(bc1.c, bc1.bc)
+```
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