Abstract: Hydraulic conductivity and diffusion coefficient are very important for the design and evaluation of landfill liner.Physical meaning and determined means of hydraulic conductivity and diffusion coefficient were analyzed.Based on microstructure analysis of porous media,the relational expression of hydraulic conductivity and diffusion coefficient was obtained.Then the equation of diffusion coefficient through bentonite was deduced using Poiseuille law.The expression is valid to some degree.It is significative to use the research result of hydraulic conductivity to study diffusion coefficient.