Abstract: As the geosynthetics are widely used in engineering practice to strengthen the slope stability, the interaction behaviors of geosynthetics and soil are very important for the slope stability analysis. A reinforced seawall constructed in coast reclamation project in Guangdong Province is analyzed. The interface friction properties of reinforcing materials and filling sand are studied by means of the laboratory shear tests and theoretical analyses, and the reinforcement mechanism is discussed. The numerical calculation is carried out on the stability and deformation behaviors of the reinforced slope under geostatic pressure. The test results show that the shear stress-shear displacement relationship of geosynthetics-soil interface is strain-harding. It is important for the stability of slope in soft foudation. In addition, the density of filling sand is the key factor for the frictional characteristics of interface. The stability analysis shows that the pavement method of reinforcing materials will directly affect the factor of safety of slope stability, and multilayer pavement effect is not a simple addition for every layer. Based on the circular slip surface method, the calculated factor of safety may be too small to reflect the contribution of geosynthetics, the strength reduction method is more reasonable for considering the interface friction. The finite element analysis also reveals that the effect of reinforcement on deformation behaviors of slope is mainly in the restriction to the magnitude of lateral deformation.