Abstract: The silicon APD performance is dependent on its device structure and processes. In this paper, the device performance and key processes for epi-planar n+-p--p+ structure silicon APD were simulated with Silvaco, in order to guide the silicon APD device design. The parameters of device processes such as ion implantation and dopant diffusion were simulated to get the impurity distribution and doping depth. Furthermore, the key parameters which were used to characterize the APD performance, such as the electric field distribution, the dark current and photocurrent, the gain, the quantum efficiency and the responsibility of the APD were simulated. The experiment results show that the maximum responsibility is up to 55A/W when the gain is 100. The device is most sensitive in the spectral range of 600 nm to 900 nm. The peak responsivity of the device is 810 nm.