Antimony sulfide Sb2S3 is an emerging photovoltaic absorber, which has been widely studied on synthesis route, device structure and interface. However, its device performance is still limited by the unoptimized Sb2S3 absorber and interface recombination, in which the neglected character of thickness is unclear. Here, the effect of absorber thickness on the Sb2S3 thin film solar cell was carefully investigated in the range of 80-620 nm, aiming to reveal the trade-off between charge separation and light absorption in the device. The characterization of JV and Sb2S3 thin film found that too thin Sb2S3 would lower the VOC and JSC, which was attributed to the severe shunt and insufficient absorption. While the too thick Sb2S3 would hinder the charge separation. This tendency was also confirmed by the performance simulation of device. Finally, the best power conversion efficiency of 4.96% is achieved with a 544 nm Sb2S3 absorber. This work provides the guidance to optimize the thickness of Sb2S3 absorber for solar cells.