Abstract: An analysis on safety factor of slope through c-φ reduction algorithm by finite elements is presented. When the system reaches instability, the numerical non convergence occurs simultaneously. The safety factor is then obtained by c-φ reduction algorithm. The factor is related to the yield criterion. This paper presented a comparison of several yield criterions in common use and deduced the substitutive relationship of them. For convenience the Mohr Coulomb criterion is replaced by Mohr Coulomb equivalent area circle criterion, which was proposed by professor Xu Gancheng and Zheng Yingren in 1990. Through a series of case studies, the safety factor of FEM is fairly close to the result of traditional limit equilibrium method. The applicability of the proposed method was clearly exhibited.