The concept of functional limit and the limit of function method is the basis of modern calculus. Thearticle summarized the defimition binary function of limit and their solving method，and explained the detail and techniques which should be paid attemtion to some specific methods. so that we can understand the function of the various limits，as well as all types of functional limit. Each method of function to limit has its advantages and disadvantages. As for the specific problem of limit，we can choose the best according to its type.