A new comparative propagation property parameter CP suitable to judge the propagation of the interface crack in the cladding part is proposed. The propagation criterion for the crack inclined across the interface is established. The theoretical research on the CPxA and CPxB of this interface crack propagating in the clad and substrate separately is carried out. The propagation law of the interface crack in the cermet cladding part is investigated with an example. The research results show that, within the ranges of the studied parameters, CPxA is bigger than CPxB, and that the crack initially propagates in the clad.