Abstract: Based on the SMP(Spatially Mobilized Plane) criterion,this article analyzes the problems of soil stress and shear strength in state of three-dimensional stress,and compares the result with the Mohr-coulomb criterion and then establishes the corresponding relationship between them.On the basis of the SMP strength criterion,the paper considered the influence on the principal stress in the soil and revised the formula of calculating slope stability.Compared the calculation results with the Swedish circle method,it is shown that using this article's formula calculates the slope's factor is smaller.