A right angle plane coordinate system that is applicable to analyze the stability of soil slopes is set up. The integral formulae of the stability analysis are obtained based on the Sweden slip circular method. It has been verified and compared with Zhang Tianbao method. The integral method based on the principle of the simplified Bishop method is presented to analyze the stability of slopes. The integral formula of the safety factor is deduced. The numerical calculation and figure treatment are programmed. An engineering example is coted to prove the correctness of this method.