The scattering phase function is an important parameter for studying the optical transmission characteristics in aerosols. Four approximate scattering phase functions commonly used in Monte Carlo simulations in atmospheric radiation propagation were compared. Aiming at the problem that the parameters of the Two-Term Henyey-Greenstein (TTHG) phase function were difficult to determine, a TTHG scattering phase function based on particle swarm optimization was proposed. This function can well fit the Mie scattering phase function, especially at backscatter angles greater than 90°. Compared with the phase functions such as HG, HG* and RHG, the phase function proposed in this paper can better approximate the actual scattering and obtain more accurate Monte Carlo simulation results.