The Cu(In, Ga)Se2 (CIGS) phase transformation during the "three-stage" evaporation is the key problem for obtaining high-quality absorber. Cu(In, Ga)Se2 (CIGS) thin film has been prepared via co-evaporation "three-stage process". The phase transformation was studied by means of XRD, XRF (X-ray fluoroscopy) and SEM. And the efficiency above 15% of CIGS film solar cell was obtained succossfully.