An interfacial crack is a common damage in a composite material structure . An extended propagation model has been established for an interfacial crack to study the dependence of crack growth on the relative sizes of energy release rates at left and right crack tips and the properties of interfacial material characterize the growth of interfacial crack better. An extended propagation model has been established for an interfacial crack to study the dependence of crack growth on the relative sizes of energy release rates at left and right crack tips and the properties of interfacial material characterize the growth of interfacial crack better.