People around the world have paid more and more attention to the problem of oil volatilization, because of the enforcement of laws on energy saving and lots of accidents caused by oil diffusion. It is important for people to find the laws of oil volatilization. That could reduce the oil diffusion during its transportation and storage, decrease the pollution, and prevent the occurrence of related accidents. Data of oil and gas diffusion in tank is obtained using the model of VOF that comes from CFD by considering the influence of wind speed, wind direction and tank type. It is also a good choice to use UDF as the source of the simulation analysis. The results show that wind speed has a great effect on oil evaporation. And the wind direction that perpendicular to the wall of the tank has evident effects. According to the study on evaporation loss of oil, the petrochemical plants must take some effective measures to reduce the oil diffusion, and reduce the risk of explosion. 