Aiming at the problem that the prediction of nitrogen dioxide gas diffusion is not accurate due to the lack of consideration of actual environmental factors, this paper proposed that rainfall and terrain can be used to study and analyze the gas diffusion. Based on the original Gaussian plume model, the rain intensity and roughness were introduced to represent rainfall and terrain respectively to carry out numerical simulation analysis. Through comparative analysis,the effects of differentrain intensities and different roughness on gas diffusion at the same altitude were first simulated, and then the relationship between downwind direction, crosswind direction and gas concentration were compared separately. Finally, the roughness and rain intensity were applied simultaneously and the results were compared with the original model. According to the experimental results, rainfall and topography affect the gas diffusion concentration and diffusion range at a certain height. Compared with the traditional Gaussian plume model, the simulation results are more practical.