An anti-reflective grating used for solar cell is proposed based on SiO2/TiO2 film to reduce its surface loss. It consists of substrate, relief structure and surface thin film. Rigorous coupled wave theory and genetic algorithm are employed to optimize the parameters such as groove depth, duty cycle, incident angle and thickness of surface thin film according to the merit function of the weighted average reflectivity. The optimized grating has the lower weighted average reflectivity than 2.16% with the incident wavelength from 300 nm to 1100 nm and the incident angle around ±40°. The lowest weighted average reflectivity is only 1.04%. Simulation results show sufficient manufacture tolerance of the designed grating.