Ductile iron has been as the materials for stamping and drawing dies due to its good mechanical properties. In recent years, laser surface modification of dies of ductile iron has been an important method to improve its wear resistance and useful life. With laser surface modification, absorptivity influences the surface modification straightly under certain laser parameters. So it is necessary to determine the laser absorptivity of ductile iron. The temperature is measured by thermal couple and treated by computer data-acquisition system. Meanwhile, the numerical simulation is to determine the absorptivity. The simulative temperature response at a certain point can be obtained through predictive absorptivity and compared with that of experiments until the simulated one is coincidence with experimental one. In the result, the absorptivities of ductile iron under atmosphere is 23.3%. It provides some reference for the selection and optimization of technical parameters during the laser material processing.