For the traditional inversion analysis method of mechanical parameters using the slope soil displacement,the objective function is too simple to represent the characteristics of the soil in the slope. In order to solve this problem,based on the traditional method, the displacement characteristics of the soil in the slope are analyzed,and the soil is divided into three categories,namely,the landslide bed,the landslide surface and the landslide body. Then,the memberships of the soil at different locations to each soil category are obtained by means of fuzzy mathematics,and the weights of each soil category are obtained via the particle swarm optimization. Moreover,a new objective function is constructed according to the memberships and the weights,which well describes the sliding characteristics of the soil at different locations. Finally,the sensitivities of the objective functions of the traditional and the proposed methods are calculated,respectively. The results show that the new objective function is more sensitive to mechanical parameters and is more effective in practice.