Abstract: A preparation method of a copper indium gallium selenide (CIGS) absorption layer, including: forming a prefabricated copper indium gallium film on a substrate; placing the prefabricated copper indium gallium film in a reaction chamber having a first temperature threshold; introducing a selenium atmosphere having a first carrier gas flow value into the reaction chamber, such that the prefabricated copper indium gallium film reacts within a first duration to form an unsaturated In—Se binary phase and an unsaturated Cu—Se binary phase on a surface of the prefabricated copper indium gallium film; introducing a selenium atmosphere having a second carrier gas flow value into the reaction chamber, such that the prefabricated copper indium gallium film reacts within a second preset duration to obtain a prefabricated CIGS film; annealing the prefabricated CIGS film within a second preset temperature threshold and a third preset duration to obtain a solar cell absorption layer.