Simplifying the form of function with the help of constructing a relevant function-k, thus providing a systematic proof for mid-value law and establishing a conventional method for mid-value structural auxiliary function. 通过构造一个对应的函数用字母k表示,化简函数的形式,给出中值定理的一种规律性证法,可以建立中值问题构造辅助函数的一般方法。