As a special soil widely distributed in the southeast coastal areas of China, granite residual soil is greatly influenced by water, leading to significant changes in its mechanical properties and greater susceptibility to disasters. To investigate the shear characteristics of the granite residual soil-geotextile interface, the effects of different moisture contents (12%, 16%, 20%, 24%) and vertical stresses (50, 100, 150, 200 kPa) were analyzed through large-scale direct shear tests. Based on the test results, the PFC2D model was established to reveal the meso-mechanism of the graniteresidual soil-geotextile interface under varying moisture content conditions during the shearing process. The results show that the interfacial shear strength and friction angle decrease with increasing moisture content, while the apparent cohesion increases first and then decreases, reaching the maximum value at a moisture content of 16%. Numerical simulation also shows the morphology of the shear zone and the displacement of soil particles. The presence of geotextile prevents the penetration of force chains between the upper and lower sections, and the primary directions of normal and tangential contact forces remain consistent under different moisture contents. Energy dissipation mainly occurs during the sliding between soil and soil particles.