In order to find the measures of preventing soil losses based on the soil mechannics, shear strengths of undisturbed and remolded soils of five typical vegetations in Jinyun Mountain of Chongqing city were measured using direct shear apparatus. Through the comparing of shear properties of undisturbed and remolded soils with the same dry density, water content and vegetation at the same vertical load, the effect of roots(the smallest roots) in soil-root composites(undisturbed soils) was analyzed. Results indicate that undisturbed soils have higher shear resistance and less shear displacement than remolded soils which have the same dry density, water content and vegetation at the same vertical loads. Shear failure of undisturbed soils approximately belongs to plastic failure, while shear failure of remolded soils is elastic failure. Shear strength of undisturbed soils has positive correlation with root content, and relevant regression models about undisturbed soil were established.