The study takes an accident of liquid ammonia leakage occurred in a chemical plant in southwestern China as a typical case, to predict its environmental consequence by using Gaussian Plume Diffusion model and divide the impacted area into the high-risk area, middle-risk area and low-risk area. On this basis, Pathfinder software package is used to simulate the emergency evacuation path for the enterprise’s employees, and identify the evacuation time. The result shows that all the employees can be successfully evacuated outside the plant within certain time period corresponding to the three risk area, i.e., 92s, 245s, 561s for the high-risk area, middle-risk area and low-risk area, respectively. The study provides insight into decision support for the design of emergency contingency plan, to minimize casualties caused by the sudden safety accidents.