According to the techniques of the mashing and the Gaussian plume modeling, combining all kinds of the factors variation, such as the tanks leak velocity, the leak height, the wind direction and speed, and the environmental stabilization grade, the concentration distributing rules of the toxic gas continuous diffusion in the tank farm are simulated. Firstly, focusing on the central of the tank farm in chemical industrial park, mashes the tank farm as the research units for quantitative analysis and superposition calculation. Secondly, constructs the diffusion concentration distributing model of the toxic gas leak based on the Gaussian plume theory. Finally, by the condition of the single-leak hazard installation and the multiple-leak major hazard installations, the toxic gas continuous diffusion algorithms are studied, viz. in accordance with any of the influence factors variation, carve up the time sections, and then basing on Matlab technique, integrating the concentration superposition effects, simulate the concentrated distribution process of the noxious substance during the influence fields. Taking ammonia gas tank farm leakage as example, the simulation results show that the method may provide technological support for major hazard prevention and control in chemical industry park.