The stability of rock slope is a long-standing problem in the field of rock mechanics. The slope stability analysis based on the finite element strength reduction method has developed from the traditional shear strength reduction method which only considers the internal friction angle and cohesion to the multi parameter coordinated reduction method including deformation parameters and strength parameters. According to the research results of finite element strength reduction method and its shortcomings, considering the increasing relationship of elastic modulus along the depth of rock mass, based on Hoek Brown criterion, a reduction scheme for elastic modulus is proposed. Combining with the slope calculation example, the finite element model is established by ANSYS, and the progressive deterioration failure of rock slope is simulated by taking the plastic zone penetration as the slope instability criterion. Compared with the safety factor obtained by traditional shear strength reduction method, it is proved that the proposed reduction method is feasible for slope deterioration reduction calculation.