Based on the strength reduction method,the anchor reinforced slope has been simulated by elastic-plastic FEM. The safety factor of reinforced slope with anchor was gotten by heuristic search method. The plastic zone running through or not is taken as a standard to solve slope safety factor. The research results show better the distribution situation of stress and strain in slope. It proposes a new method to evaluate the stability of slope with complex boundary conditions. Taking a slope engineering for example, the stability safety coefficients of the slope are calculated when the slope is reinforced with anchors of different length. When the design length of anchor is longer than a certain value, the anchor length has little effect on improving the stability of slope and slope toe. Consequently, the reasonable design length of anchor is put forward