In this paper, the light trapping characteristics of glass substrate with hemisphere pit (HP) arrays in thin film Si solar cells are theoretically studied via a numerical approach. It is found that the HP glass substrate has good antireflection properties. Its surface reflectance can be reduced by～50%compared with planar glass. The HP arrays can make the unabsorbed light retu to the absorbing layer of solar cells, and the ratio of second absorption approximately equals 30%. Thus, the glass substrate with the hemisphere pit arrays (HP glass) can effectively reduce the total reflectivity of a solar cell from 20%to 13%. The HP glass can also prolong the optical path length. The numerical results show that the total optical path length of the thin film Si solar cell covered with the HP glass increases from 2ω to 4ω. These results are basically consistent with the experimental results.