Abstract: Under rainfall the vegetated slope often slides along the soil layer below the root system. The main reason is that the root system is shorter than the influence depth of the rainfall, and the mechanical reinforcement is insufficient to effectively protect the slope soils. In order to compensate and improve the capability of the mechanical reinforcement of short roots to resist-rainfall induced landslides, the vertical geotextile belts can be arranged in the slope. A large-scale direct shear test device is designed to explore the reinforcement effect of the root system and geotextile belts on the mechanical strength of soils. The direct shear tests on the root-soil composite with different inclinations (0°, 30°, 45°, 60°) and the belt-soil composite with different moisture contents (0%, 5%, 10%) and different numbers of belts (0, 2, 4, 6, 8) are carried out. The results show that the root system can significantly increase the mechanical strength of the soils. With the increase of the root inclination, the tensile deformation increases, and the shear strength of the root-soil composite increases. The greater the initial inclination of the root along the shear direction is, the smaller the shear displacement occurs when the root fractures. The interfacial shear strength of the belt-soil composite is affected by the moisture content of the soils, the number of geotextile belts and their dry and wet state. The strength decreases with the increase of the soil moisture and increases with the increase of the number of belts. Under the moisture content of 5% in the soils, the cohesion and internal friction angle of the wet geotextile belts are significantly lower than those of the dry ones. The test results provide theoretical reference for the application of geotextile belts in the vegetated slopes, which is beneficial to prevention and control of shallow landslides.