It is of primary importance to estimate the crack size on the interface of two solids for evaluating the integrity of jointed interfaces. In this paper, the scattering problem of elastic waves is formulated for the interface crack of layered materials in water. Green’s function for the water/solid/solid material is constructed and utilized to represent the scattered pressure field in water caused by the crack opening displacement in the interface of two solids. Introduction of the far-field approximation for the scattered pressure field and then the high frequency approximation for the crack opening displacement leads to a simple equation which is related to the crack size, the wave velocity in water, the angles of incident wave and observation point, and the period of scattering amplitude in the frequency range. The size of interface crack is estimated by measuring the periodicity of the scattering amplitude for fixed transducer’s angles in water. Examples are shown for pulse-echo configurations.