Abstract: In order to provide the technical aid for chemical leakage accidents in factory, taking the zone of benzene tank in He’nan Shenma Nylon Chemical Co. as a sample, the heavy gas dispersion model and turbulence flow model were used to simulate leakage of benzene tank under the constrain of basic assumptions. The gas concentration contours with the change of wind velocity were analyzed and the safety zones were determined. The results of simulation show that the bands of diffused puff are formed along the direction of tailwind and the rate of vertical or horizontal proliferation is equal in mixed layer. For different wind speeds, appropriate protective measures should be taken to control the results of accident. The achieved visual simulation and function of onsite data management provide the technical support for the leak accident of benzene tank.