Abstract: Enhancing optical absorption is an important way to improve the photoelectric conversion efficiency of solar cells. A new metal grating-based solar cell structure was designed. The absorption spectrum and enhancement factor were calculated by rigorous coupled wave analysis (RCWA) method. The influences on optical absorption induced by the grating width, the angle and polarized states of the incident light were discussed. The results show that the optical absorption factor in the designed structure can be greatly enhanced up to 40% when the incident wave is transverse magnetic (TM) polarized, and nearly 16% under other incident waves condictions. These indicates that the new solar cell structure can significantly improve the overall optical absorption compared to bare a-Si thin film solar cells.