A new method for analysis of slop stability to earthquake is presented. The method combines finite element method (FEM)with traditional slip surface method, and is divided into two steps: first, based on the FEM, the effective stresses in slop are determined by solving dynamic equilibrium equation at some time; second, determining the most dangerous slip surface and its factor of safety at this time by using the effective stresses calculated in the preceding step. The method not only can consider behavior of stressstrain of soil, but also can determine the most dangerous slip surface and its factor of safety at any time. The detailed algorithm of the method is also given.