Abstract: Process in the leakage diffusion, oil pool extending, oil volatilization and vapor cloud dispersion for oil pipeline are analyzed, and the mathematical models for different physical transversions are discussed. In order to describe the characteristics of longtime continuous dispersion of the vapor cloud from the oil pool, the area source dispersion model is built based on Gauss plume dispersion model. By calculating the volatilization rate and the range of dangerous vapor cloud for a typical leakage accident of pipeline, the effects of temperature, wind speed and atmosphere stability about the vapor cloud are analyzed. The result shows that an explosive vapor cloud that covers much larger area than that of the pool will produce from volatilizing under stable atmosphere convection and static wind after the formation of oil pool of volatile oil like gasoline.