Abstract: Based on upper bound theorem of energy method,and concerning the sliding body of soil slope as deformable body,the calculation formula can be deduced according to proper combination of energy method strength reduction method. The difference between energy method and traditional rigid limit equilibrium method shows in two aspects:firstly the former uses energy balance,whereas the latter uses static balance;secondly,the former treats sliding body as deformable body,whereas the latter treats sliding body as rigid body. Through a typi-cal case study,the calculation results show that the safety factor of energy method is smaller than rigid limit equilib-rium method.