In the fabrication of photodiode of monolithic integrated photoreceiver using laser induced diffusion, because the high temperature region is very small, when the intensity distribution of incident laser beam is Gaussian or uniform, the uniformity of the temperature distribution in the diffusion region cannot meet the requirement of uniformity. In this paper, a method to homogenize the temperature through modulating of the intensity incident on the surface using a mask is proposed. The key of this method is calculating the laser intensity distribution, which can induce uniform temperature rise in the diffusion region. The numerical method to solve this problem is described. The results show that when the mean temperature rise in the diffusion region is about 500 K, the maximum temperature difference of 3.9 K can be achieved, and the temperature distribution approaches “flatcap”.