Objective For understanding the biophysical process of T-cell immune response, to reveal the diffusive features of the adhesion molecules in the complicated topographic cell contact area, and develop a method to estimate the diffusive coefficient. Method In this paper, by taking an account of the crowding effect of the adhesion molecules, we present a porous structural model of the cell contact area, and derived the diffusion equation of the free ligand molecules on the cell contact area. In the cases of the cell contact area being the isotropy porous structure, the diffusive damping factor γ is related with the obstruct density σ by an analytical expression, and in the case of axial-symmetry, the logarithmic distribution character of γ is obtained too. Results The retardation of the free ligand diffusion will be strengthened as increasing of the diffusive damping factor γ and decreasing of the obstruct density σ in the contact area, and using FRAP experiment data, the parameter α, γ and ξ have been estimated as 0.2~0.4, 0.40~0.56 and 0.73~0.75 for the adhesion system of CD2/CD58 and CD28-CD80, respectively. Conclusion A new method to estimate the diffusive retardation coefficient ξ of the adhesion molecules by measuring the fluorescence recovery level on the photobleaching region of the contact area is proposed.