In the failure process of slopes, the contribution of different mechanical or material parameters to the stability is different and dynamic. In the context of shear strength reduction method (SRM) for stability analysis, it is of great significance to determine the factor of safety (FOS) by considering non-proportional reduction for these different mechanical or material parameters. This study firstly examines the mechanism of energy evolution in the process of slope failure. Then, the contribution of different mechanical parameters to dissipated energy evolution is weighted in conducting SRM, based on which we proposed a new method to calculate the FOS with multiparameter non-proportional reduction of shear strength parameters. This method can reflect the characteristic of FOS following the whole reduction path of different shear strength parameters. Subsequently, the proposed method is verified by examples. Finally, the influence of the reduction step and reduction path of the non-proportional reduction factors on the calculated FOS results is discussed.