Spill of volatile poisons into natural water bodies causes water pollution and then air pollution arises from water pollution because of volatilization. In order to explain the coupling of water pollution and air pollution, the dimensionless Henry constant of volatile poisons was used to establish coupling diffusion model based on compressed VOF method and the double film theory explained for volatilization. A high resolution bounded differencing scheme for arbitrarily unstructured meshes was applied to simulate coupling diffusion of trichloroethylene and tribromoethylene. The simulation results are in good agreement with those from single phase model. The influence of environmental temperature, wind velocity and the dimensionless Henry constant on the mass transfer across gas liquid interface was analysed.