In this study, we present an effective method of improving the performance of pure sulfide Cu(InGa)S-2 (CIGS) solar cells via injection annealing system. The injection annealing system can perform annealing at desired temperatures, and therefore, the CIGS thin film passed over the temperature range in which secondary phases occurs. Via the injection annealing system, secondary phase InSx was effectively removed from the surface of the CIGS thin films at the temperatures over 550 degrees C. This resulted in the formation of good-quality P-N junction CIGS devices, thereby improving significantly the performance of the CIGS solar cell. In addition, the open-circuit voltage (V-OC) and fill factor (FF) of the CIGS devices increased gradually with increasing annealing temperature in the range of 550-640 degrees C. It is speculated that the bulk defects were decreased as the annealing temperature increased. Finally, via injection annealing system, a pure sulfide CIGS solar cell with an efficiency of 12.16% was achieved.