In the presence of Se, Cu(In0.7Ga0.3)Se2 (CIGS) thin films are prepared by the sequential evaporation of Ga, In, Cu at a constant substrate temperature between 250 ℃ and 550 ℃ on the Mo/soda lime glass substrates. The thickness values of films are about 0.7 μm. The structural and phase properties of CIGS films are studied by an X-ray diffractometer, the morphology and crystalline quality are characterized by a scanning electron microscope, the depth profiles of elements are measured by a secondary ion mass spectroscopy, the surface compositions are analyzed by a Raman spectrometer, and the optical properties of CIGS films are measured by a spectrophotometer with an integrating sphere. It is found that the films prepared at substrate temperature above 450 ℃ each exhibite a single Cu(In0.7Ga0.3)Se2 phase, and the homogenization of Ga/(Ga+In) distribution in the Ga-In-Se precursor is achieved by the diffusion of In atoms through grain boundaries. As the substrate temperature is less than 400 ℃, a serious Ga phase separation is observed and the high content of Ga phase mainly exists at the top and bottom of CIGS films. Below 300 ℃, a serious deterioration of crystalline quality is found, and Ga atoms cannot effectively enter into the CIS lattice position to form CIGS. The films prepared at the substrate temperature less than 400 ℃ are covered with lots of Cu(In0.5Ga0.5)Se2 small grains, which results in the enhancement of the surface roughness and the formation of a light trapping structure at the interface of Cd/CIGS. Thus, the light absorption of solar cell is improved. In addition, the smaller gap value of the low Ga content phase also facilitats the light absorption, then the short-circuit current density of thinned solar cell is greatly improved. The analysis shows that the short-circuit current density is the main factor affecting the conversion efficiency of thinned solar cell prepared between 550 ℃-350 ℃. However, when the substrate temperature is below 350 ℃, the reduction of VOC and FF has become the main reason for the deterioration of solar cell. In conclusion, the efficiency of solar cell with 0.7 μm CIGS absorber prepared at substrate temperature of 350 ℃ reaches 10.3% due to the improvement of short-circuit current density.