The diffusing non-contact measurement method is effective for measuring incident laser power density. However, the strong laser irradiates diffusing metal plane for a long time, which once makes the temperature of target plane rise to a degree, causing the surface reflection descend significantly. The measuring results are affected. Based on the finite element method, considering hot source and wind convection, the temperature changes of Al plane coated Au film are simulated under strong laser irradiation, the results show that the energy absorption is the key factor to temperature rising. The energy absorption of diffusing surface can be designed similar to smooth surface, reducing the temperature of target plane effectively. the optimum design reference for diffusing metal target plane is provided.