Ammonia is a colorless and toxic gas. Due to its fast leakage rate, the leakage port is not easy to detect, and it is often difficult to seal it, causing more serious personal injuries and property losses. So it is a key problem to predict the intensity and location of toxic and harmful gas leakage quickly and accurately. Then it needs to combine the atmospheric diffusion model and optimization algorithm to establish the source term information back calculation model, and solve the location and intensity of the leakage source based on the concentration data of the downwind direction of the leakage source. Based on the analysis of the physical and chemical properties of ammonia, according to Wilson plume rising experience formula and Gauss plume model, the leakage model of liquid ammonia storage tank is established, and the effective monitoring points are extracted. According to the concentration of simulated monitoring points, the source information is calculated by particle swarm optimization algorithm. The feasibility of this method in the leakage of liquid ammonia storage tank is verified, which can help emergency response of accidents.