Abstract: Taking a platform in East China Sea as an example, the method of numerical simulation was used to study the diffusion law of combustible gas under different conditions. The k-epsilon model was used to describe the turbulent motion of the gas phase, and the Species Transport model was used to describe the combustible gas diffusion process. The results showed that the diffusion of cold venting exhaust gas was less affected by the environmental wind direction. The diffusion of cold venting exhaust gas was significantly affected by wind speed conditions and venting rate. As the ambient wind speed increased, the combustible gas cluster formed near the torch head became smaller and the center of the combustible gas cluster became closer to the torch head. With the increase of the discharge rate, the larger the combustible gas cluster formed near the torch head, and the center of the combustible gas cluster was farther away from the torch head. Under the conditions of accidental extinguishing, fire and blocking, the corresponding maximum diffusion distances were 15.69 m, 20.62 m and 28.48 m, respectively. The safe flight distances of helicopters away from the torch head were 16 m, 21 m and 29 m respectively. It was suggested that the platform should strengthen the maintenance of combustible gas detection system to ensure timely detection of cold venting gas.