In order to study the influence of Ag nanowires on the light absorption efficiency of crystalline silicon thin film solar cells, a kind of crystalline silicon thin film solar cell structure with triangular grating and rectangular grating at fixed volume ratio was designed. At the Ag-Si junction of the two structures, a circular and rectangular Ag nanowire array were added respectively. The absorption spectra of these two structures and the control group were simulated by finite difference time-domain method. The optimal height, nanowire cross-sectional area, and distribution density of the two grating structures were obtained by sweeps function of finite difference time-domain method software, and the light absorption efficiency of wavelength region of 300~1 100 nm was calculated under the optimal conditions. The absorption enhancement mechanism of the nanowire model in the long wavelength band was obtained by analyzing the light absorption enhancement spectra and the electromagnetic field intensity distribution. The results showed that the two structures with Ag nanowires had better light capture and absorption than the two control groups. Moreover, the absorption efficiency of Ag nanowires in the rectangular grating model is improved more significantly than the triangular grating model, which can provide reference for the design of structural parameters of new solar cells.