If the numerical method of slope stability analysis is based on global strength reduction and local strength reduction method， it can only obtain a single slope safety factor and the numerical reference value of slope in critical instability. In order to analyze the stability of the slope and make the analysis result more accordingly with the actual project condition， through the extrusion function and the designed program by FLAC3D， this article realizes the control of reduction area， strength reduction calculation precision and strength reduction coefficient range. In this paper， the typical earth-rock mixed high slope is the research object， through building a three-dimensional numerical model of slope. Firstly，the slope intensity change area is defined. Secondly，the calculation accuracy is confirmed. Then， strength reduction coefficient range is adjusted according to the actual working conditions. Finally， the stability analysis of earth-rock mixed high slope is realized. The analytical results obtained by the method are in accordance with the actual engineering conditions. The calculation results of the project show that，the numerical method reflects the deformation and failure characteristics and the area of sliding surface in the various stages of the construction. Compared with the traditional stability analysis method， it can better quantify the deformation and failure state of the slope. The results can provide an effective reference for the stability analysis of earth-rock mixed slope.