In order to improve the short circuit current density and conversion efficiency of crystalline silicon thin film solar cells, a silicon dielectric grating and an aluminium metal grating were integrated on the front and back of single crystal silicon thin film solar cells respectively. The effect of the period, thickness and duty cycle of both the gratings on the short-circuit current density and optical conversion efficiency of single crystal silicon thin film solar cells were simulated with finite difference time-domain software. The results show that, the short-circuit current density can reach 35.15mA/cm2 and the conversion efficiency is 43.35% when both the front and back gratings are at the optimum value (for the dielectric grating, duty cycle F=0.8, period P=0.632μm, thickness hg=0.42μm; for the metal grating, duty cycle F1=0.9, period P=0.632μm and thickness hm=0.005μm). After comparing the optimal grating monocrystalline silicon thin film solar cells with traditional monocrystalline silicon thin film solar cells, the grating monocrystalline silicon thin film solar cells have a significant improvement in both optical path and absorption efficiency. This study provides theoretical guidance for the preparation of high performance thin film solar cells in the future.