Abstract: Effective modulus theory is effective only for non-uniformity rocks with a macro-continuous variation. A distortion or mistake can be caused by the application of effective modulus theory in the wave propagating rule study, if there are interfaces in the rocks. Experiments show that the flexibility coefficient which represents the characterization of discontinuity interfaces has an influence on elastic wave propagations. Propagating rules of the elastic wave cross the interfaces in oil and gas reservoir media are theoretical analyzed, reflect and transmit coefficients of a spring model and a Maxwell model are derived, and relevant change rules are obtained about relations between the flexibility coefficient and reflect, transmit coefficients, energy losses, as well as the total reflect.