The change of temperature rise caused by 1064 nm long-pulse laser irradiation on Si avalanche photodiode (Si-APD) is studied theoretically and experimentally. Considering the Si-APD multilayer structure, we establish a two-dimensional axisymmetric heat conduction model, and simulations under different conditions are carried out. We carry out the experimental study on temperature rise of Si-APD irradiated by long-pulse laser. The simulation results are consistent with the experimental results, which shows that the temperature rise caused by the interaction between long-pulse laser and Si-APD is determined by the energy density and pulse width of incident laser.