The model of copper-antimony-sulfur (CuSbS2) thin film solar cell was constructed, and the performance of the device was calculated by SCAPS. The effects of absorption layer thickness, carrier concentration, defect density, and back contact work function on the device performance were investigated. The results show that the green and red light are not fully absorbed by too thin absorption layer, and the absorption layer with the thickness of 1.5 μm to 3 μm can meet spectral absorption requirements. When the acceptor concentration is 2×1018 cm-3, the photoelectricity conversion efficiency (PCE) of the device is the highest. When the defect density is larger than 10-14 cm-3, the PCE of the device decreases sharply. CuSbS2 prepared in a copper-poor and sulfur-rich atmosphere can increase the accepter concentration, reduce the open circuit voltage defect, and inhibit the formation of sulfur vacancy defects, thus improving the PCE of the device. High work function materials can decrease the back contact barrier and reduce carrier recombination. After the material parameters have been optimized, the highest PCE of the device is 21.74%.