Abstract: As the Loess Plateau is the most frequently affected area by landslides in China, and rainfall is the main influencing factor for the scour and instability of loess slopes, so it is particularly important to understand the law and mechanism of water infiltration on the surface scour of different slopes and inside the slope body. In this paper, the slope soil we studied is from Heifangtai loess in Gansu Province. Indoor triaxial shear tests were carried out on loess with different water contents. Rainfall scour tests and model box slope water holding capacity monitoring tests were designed and carried out under different vegetation protection. Sensors were used to monitor the volumetric water content and matrix suction of the slope. The displacement of the slope under different rainfall intensities were measured and analysed, and the flow and sand production of different vegetated slopes were recorded. The results are as follows: The cohesion and internal friction angle of the soil body show a quadratic function with the water content. The bare slope has the shortest flow production time, the least water infiltration, and the slope surface is relatively easier to produce runoff, thus entering the slope erosion stage. The increase in slope gradient leads to an increase in slope runoff velocity, which strengthens the water resistance of the slope surface, and the slope erosion decreases with the increase in slope gradient. The decrease of the matrix suction of the soil body under the effect of heavy rain and rainstorm is significantly faster than that under the effect of light rain and medium rain. The stable value of matrix suction is the largest under light rainfall and the smallest under heavy rainfall.