Abstract: Based on the work conducted by Sørensen etc., a method for determining interfacial traction-separation law with dilatancy was presented to investigate interfacial cracking processes of composites. The tangential traction-separation law was derived via a pre-defined shear dilation function and the normal traction-separation law while the interface was in tension. On the contrary, the tangential traction was decomposed into bond strength and friction strength while the interface was in compression. The friction strength is related to the normal pressure and the damage process on the cohesive interface. The results of the method explain why the tangential traction-separation law of Sørensen model is not continuous and violates the consistently coupled rule. In order to facilitate numerical simulation, expressions of interface stiffness matrix applying to three dimensional finite element models were also presented. Then a particular shear dilation function was adopted and the normal traction-separation law was assumed as multilinear form and exponential form, respectively. The corresponding tangential traction-separation law was derived applying the method presented in this paper to those functions. Finally, two examples of engineering application were given. These numerical simulation results are in good agreement with the experimental data.