Earth-abundant ternary Cu2SnS3 (CTS) thin films have attracted lots of attention as promising solar cell materials. However, the performances of the related devices were limited by the coexistence of different polymorphic phases and the poor quality of the sulfurized CTS films. It is well known that these two key factors are mainly dependent on the heat treatment temperatures. In view of this, CTS films were prepared via a simple sol-gel method followed by rapid sulfuration process and the effects of the annealing temperature on the crystal structure, morphologies and the photoelectrical properties of samples were discussed in detail. The results indicate that higher quality films with suitable properties can be obtained by annealing at 560 degrees C. More importantly, a phase transition from cation-disordered cubic structure to cation-ordered monoclinic structure was observed with the increasing temperature, which led to a reduction of the deep-level defects in the bulks of the films. Benefit from both of these effects, the efficiency of the CTS solar cells showed a significant improvement from 1.78% to 3.16% due to the enhanced open-circuit voltage (V-oc) and fill factor (FF).