Abstract: Destruction of slopes and their protection engineering are often cause by rainfall. For the implementation of ecological restoration project on the shorelines in our country, using the root system of (10 + 10) g/m2 Agrostis stolonifera + Paspalum notatum Flüggé grown for 12 months as an example, the mechanism of soil reinforcement and slope protection of herbaceous plant roots in the advanced rainfall pattern is researched. In the paper, the advanced rainfall pattern is simulated for the deformation of slope and the variation of the water content, pore pressure and suction. The expression of the relation of hydraulic characteristics of bare soil and root soil. A new stability analysis model under rainfall at a specific time is proposed for explaining the impact of depth and rainfall duration on stability factor. The results show that (1) in the advanced rainfall pattern, the stability of the soil slope is more susceptible to the effects of the early 150 mm/h rainfall compared to vegetated slopes, and the impact of subsequent 50 mm/h rainfall on the stability of the vegetative slope is relatively minor; (2) herbaceous roots improve the stability of 30 cm depth of root soil layer, deteriorate the stability of 35 cm to 60 cm soil medium layer near root soil layer. The deeper than 100 cm soil layer is lightly influenced by roots; (3) herbaceous roots can prolong the stability of slope, reduce soil erosion, and protect soil and water. However, herbaceous roots should work with other engineering structures for the long-term stability of bank slope. The paper provides necessary data and theories for the construction of ecological bank protection projects in the middle and lower reaches of the Yangtze River.