A method for fabricating a Cu-In-Ga-Se film solar cell, characterized in, comprising: a) fabricating a molybdenum back electrode on a substrate; b) fabricating a Cu-In-Ga-Se absorbing layer on the molybdenum back electrode by a vacuum magnetron sputtering with CuIn x Ga 1-x Se 2 alloy targets, wherein the CuGaSe 2 alloy target where x=0 is a first target, and the CuIn x Ga 1-x Se 2 alloy target where x ranges from 0.6 to 0.8 is a second target, then firstly a sputtering with any high power density ranging from 4W/cm 2 to 8W/cm 2 is performed with the first target for 2-4 minutes, then a co-sputtering is performed with the first target and the second target for 30-60 minutes, in which the first target works with a power density continuously decreasing from any high power density ranging from 4W/cm 2 to 8W/cm 2 to any low power density ranging from 0.3W/cm 2 to 1W/cm 2, and the second target works with a power density continuously increasing from any initial low power density ranging from 0.3W/cm 2 to 1W/cm 2 to any high power density ranging from 4W/cm 2 to 8W/cm 2, so that a Ga concentration in the Cu-In-Ga-Se absorbing layer has a gradient, the Ga concentration has a maximum on a surface of the Cu-In-Ga-Se absorbing layer contacting with the molybdenum back electrode and has a minimum on the other surface of the Cu-In-Ga-Se absorbing layer; c) performing an annealing for the Cu-In-Ga-Se absorbing layer in a rapid heating mode in a vacuum chamber under a temperature of 400-600 °C for 55-90 seconds; d) fabricating an In 2 Se 3 or ZnS buffer layer with a thickness of 80-120nm on the Cu-In-Ga-Se absorbing layer; e) fabricating an intrinsic zinc oxide high impedance layer with a thickness of 0.1-0.5μm on the In 2 Se 3 or ZnS buffer layer; f) fabricating an indium tin oxide film low impedance layer with a thickness of 0.3-0.8μm on the intrinsic zinc oxide high impedance layer; and g) fabricating an aluminum electrode on the indium tin oxide film low impedance layer. a) fabricating a molybdenum back electrode on a substrate; b) fabricating a Cu-In-Ga-Se absorbing layer on the molybdenum back electrode by a vacuum magnetron sputtering with CuIn x Ga 1-x Se 2 alloy targets, wherein the CuGaSe 2 alloy target where x=0 is a first target, and the CuIn x Ga 1-x Se 2 alloy target where x ranges from 0.6 to 0.8 is a second target, then firstly a sputtering with any high power density ranging from 4W/cm 2 to 8W/cm 2 is performed with the first target for 2-4 minutes, then a co-sputtering is performed with the first target and the second target for 30-60 minutes, in which the first target works with a power density continuously decreasing from any high power density ranging from 4W/cm 2 to 8W/cm 2 to any low power density ranging from 0.3W/cm 2 to 1W/cm 2, and the second target works with a power density continuously increasing from any initial low power density ranging from 0.3W/cm 2 to 1W/cm 2 to any high power density ranging from 4W/cm 2 to 8W/cm 2, so that a Ga concentration in the Cu-In-Ga-Se absorbing layer has a gradient, the Ga concentration has a maximum on a surface of the Cu-In-Ga-Se absorbing layer contacting with the molybdenum back electrode and has a minimum on the other surface of the Cu-In-Ga-Se absorbing layer; c) performing an annealing for the Cu-In-Ga-Se absorbing layer in a rapid heating mode in a vacuum chamber under a temperature of 400-600 °C for 55-90 seconds; d) fabricating an In 2 Se 3 or ZnS buffer layer with a thickness of 80-120nm on the Cu-In-Ga-Se absorbing layer; e) fabricating an intrinsic zinc oxide high impedance layer with a thickness of 0.1-0.5μm on the In 2 Se 3 or ZnS buffer layer; f) fabricating an indium tin oxide film low impedance layer with a thickness of 0.3-0.8μm on the intrinsic zinc oxide high impedance layer; and g) fabricating an aluminum electrode on the indium tin oxide film low impedance layer.