The unscience and the properties of multisolution of the value of c and φ by graphic solution, and the advances (unique) and lacks (mechanism) of the value of c and φ by standard(GBJ7-89) are analysed in this paper. A new method to determine the value of c and φ by using the absolute value of the least relative error is proposed,The reliability of the value of c and φ are improved by this method.