中文摘要：

利用微分中值定理得到了分段函数在分段点可导性的一个判别方法，进而得到分段函数的导函数的两个性质，最后举例应用．

英文摘要：

An estimation method is obtained by the differential mean value theorem to solve the differentiability of sub-function, and two properties of derivative function are obtained by this method Finally, examples are given to apply this method.