Dugdale-Barenblatt model is extended to analyse the problem of the crack on the interface between two viscoelastoplastic materials. After the governing equations are Fourier-transformed, the problem of boundary conditions with tangential jumps trans-formed into singular integral equations by using sectional definite-integral transformation. Following solving the integral equations are the formulation of the length of the plastic zone (LPZ) ahead of the crack tip and crack-tip opening displacement (COD), and the derivation of the strain energy release rate. Results reveal that the LPZ and COD are both determined by the minimum yielding stress of the two constituent materials, and the latter also rises at a gradually declining speed as time increases.