The work aims to improve the absorptivity of the high reflectivity material aluminum alloy by laser cutting. Based on the principle of thermal equilibrium, a test stand for laser absorptivity was set up. Such four different coating treatment methods as lusterless paint, carbolic ink, common ink and graphite were applied on the surface of 1.2 mm thick 2A12 aluminum alloy samples. CO2 pulse laser emitter was used for the test of fixed point irradiation. The temperature change of aluminum alloy samples was measured with K-type thermocouple, based on which the amount of its absorptivity was indirectly obtained. Test data showed that under certain technological parameters, with the increase of laser power or scanning time, the surface temperature of all samples was integrally increased. Among the four different surface treatment methods, the absorptivity of the aluminum alloy treated with lusterless paint was the highest, which was increased by 40% compared with the original surface. After this conclusion was applied to engineering practice, the test-piece cutting surface was smooth after machining. The slag size was small and the surface quality was high. In conclusion, this absorptivity tester and surface treatment method can successfully im prove the absorptivity of the material to the laser.