Abstract: Effective diffusion coefficient of VOCs in porous medium is an important parameter in the process of mass transfer of soil vapor extraction(SVE).To study effective diffusion coefficient and diffusion law of volatile benzene in media of fine sands different in water content,a soil column diffusion experiment was carried out.Results show that water content affected diffusion of volatile benzene to a certain extent in such a medium as fine sands containing little adsorptive clay mineral.The diffusion rate was the highest when water content in the medium was 50 g·kg^-1;When the water content was within the range of 0-50 g·kg^-1,the higher the water content,the higher the diffusion rate.But when it reached beyond 50 g·kg^-1,the higher the water content,the lower the diffusion rate.Moreover,in the same column,the effective diffusion coefficient increased along with the distance,which was possibly attributed to a decreasing fractional vapor pressure of volatile benzene.