A finite element method is presented for predicting chloride diffusion coefficient in concrete.First,concrete is considered as a three-phase composite material consisting of aggregate,interfacial transition zone(ITZ) and cement paste.By comparing two typical unit cell models the advantage of the circular unit cell model in simulating concrete is demonstrated.Since the ITZ thickness is much smaller than the aggregate size,the advancing front method is adopted to divide the unit cell as accurately as possible.The finite element method is then used to obtain the numerical solution for the chloride diffusion coefficient in concrete.Finally,the validity of the method developed is verified by comparing the numerical results with the experimental data.Based on the numerical results,the effects of maximum aggregate diameter,chloride diffusion coefficient of ITZ,ITZ thickness and aggregate gradation on the chloride diffusion coefficient in concrete are evaluated in a quantitative manner.