Augmented reality (AR) system is a display system that superimposes virtual images on the real environment. Since the optical waveguide can realize miniaturization and light weight, it is the core component of the AR display system. The diffraction efficiency of the optical waveguide coupling element greatly affects the imaging quality of the AR display system. In order to improve the diffraction efficiency of the coupling element in the AR display system, a waveguide structure with multi-layer superimposed gratings was proposed. Based on the vector diffraction theory, the grating was simulated and analyzed by using the rigorous coupled wave analysis method. Simulation results show that the average diffraction efficiency of a single-layer inclined grating reaches 60% at a field of view of 50°, and the average diffraction efficiency of a waveguide structure with three layers of superimposed gratings reaches more than 85%, which is 25% higher than that of a single-layer grating. The analysis results show that the waveguide structure with multi-layer superimposed gratings can achieve a larger field of view and diffraction efficiency, so that the AR display system has a clearer viewing field.