Well site safety plan, which included well design, emergencyresponse plan (ERP) etc, is the key prerequisite for drilling the critical sour gas well. A right emergency response zone (EPZ) is quite difficult to make sure on the site, because that it affected by release rate of H2S, gas composition, the well site surrounding topography, and other specific circumstances. To solve this problem, A blowout simulation software based on FLUENT be developed, which could predict affected areas when the critical sour blowout, the gas flow direction, and the H2S concentration distribution. On this basis, the safety layout surrounding the well site can be planned. The article provides the design structure and main functions of the software. The software can provide the theoretical basis of industrial safety.