Abstract: The sorption has major influence on organic pollutant biodeg radation in soil/water system.It is found that the bioavailability of organic pollutant,as well as the fraction of organic pollutant exists in the aqueous phase at sorption equilibium,decreases along with the increase of soil-water partition coefficient K_d,or the increase of soil-water ratioin the system.A spherical model has been developed in this paper in order to describe quantitatively the effect of sorption on the transport of organic pollutant in side the soil particle.It is noteworthy that the overall organic biodegradation rate in the system is controlled by its sorption capacity.Chemical with a large K_d value with chemical will have low transport rate and low biodeg radation rate in soil/water system.