On the base of studying the mechanism of the material strength on slope stability, combining a simple uniform slope and a non-uniform slope study, the plaxis software based on the strength reduction theory and the geo-studio software based on limit equilibrium theory were used for calculation. The material parameters impact on slope safety factor and slip surface was analyzed by using the Mohr-Coulomb constitutive model. The results show that: (1) when λcr is constant, changing cohesion c and internal friction angle had no effect on the sliding surface; when the λcr changes from small to large, the sliding surface changed from light to dark, and the import and export moved away from the top and base; while when the λcr changes from large to small, the sliding surface changed from dark to light, the import and export moved near the top and base; (2) the safety factor and the cohesion force c were approximately linearly increasing, and the internal friction angle was nonlinearly increasing; (3) the safety factor decreased with the increase of the slope angle or slope height, but its impact on slip surface was the same as that of conclusion (1).