The disadvantage of the traditional slices method is that the shear strength of all the soil in the slope is calculated according to the boundary state of stress. In order to address this problem, according to the mechanism of progressive failure, the partition calculation model is proposed in this paper. According to the mechanical analysis, the model searches three regions of the slope: instability region, critical region and stable region, and calculates the corresponding shear strength according to the true stress state of each region. Finally, the model analyzes the slope stability. In this paper, the stability analysis software is developed based on partition calculation model. Through theoretical and case analysis, it can be found that partition calculation model is more in line with the engineering practice. When there is instability region in the slope, the safety factor calculated by partition is smaller. When the whole slope is stable region, the safety factor calculated by partition calculation method is the same as that calculated by Fellenius simplified method. And partition calculation model can guide slope reinforcement more economically and effectively.