Abstract: A coupled multiphase flow model was established to predict transient flow and petroleum pollutant transport in subsurface environment.The model accounted for the complex process of dispersion, absorption/desorption,distribution between liquid-solid interfaces and microbiological degradation under the assumption of local chemical equilibrium.Solutions of the coupled equations were accomplished by the characteristic finite difference method and implicit pressure explicit saturation method.The code was developed for simulating petroleum pollutant transport and migration mechanism in porous media.Numerical results showed petroleum pollutant leaking into subsurface environment,with vertical and horizontal displacement under gravity and capillary pressure.As pollutant migrated into the capillary zone,capillary tension restricted the vertical movement.The pollutant must overcome the entrapment pressure of oil-water interface before entering the capillary zone, and pollutant accumulated on the top of the capillary zone to become pressurized.The pore pressure of pollutant exceeded the entrapment pressure of oil-water interface,and pollutant entered the capillary zone and formed a lens above the groundwater level. The model simulations were compared with experiential measurements of petroleum pollutant mass distribution in soil, and there was reasonable agreement between model simulation and measured data.It provides theoretical evidence for studying distribution and destination of organic pollutant transport in subsurface environment.