Plane sliding is a simple form of the rock slope sliding. Insufficient homogeneous rock slope due to shear plane sliding is the major object of study. By assuming the iteration of the relationship between the failure surface and the angle of internal friction, we obtain the safety factor. Considering the limit equilibrium, using different reduction methods and reduction factors with are compared with those of the finite element method, we obtain the relationship among all physical quantities, and find the main reference for determining the doublestrength reduction factors, which may serve as reference for further study of the field.