Abstract: The distribution of plant roots is an important factor affecting slope stability under rainfall conditions by more and more studies. In order to study the influence of different types of roots on slope stability indoor simulated rainfall experiments were accomplished, to analyze the influence modes of different types of plant roots and explore the influence mechanism of root characteristic size and distribution. Results show that in the process of soil deformation the small discontinuous pores in the slope is easy to close and block automatically and not easy to form new local failure. Furthermore, woody plants with coarse roots have adverse effects on slope stability and the local failure is likely to occur at the location of plant roots contacting with soil, but roots of herbaceous plants have a significant strengthening effect on soil and its effects are confined to a certain range. It reveals that there is geometric scale and spatial distribution features for the effects of plant roots on slope, while the root system has the most significant effect on preventing slope instability when it is distributed near the initial point of potential sliding surface. The research results provide a reference for the influence mechanism of plant roots under rainfall conditions.