The study focuses on the propagation of SH waves in an elastic plate whose material properties are sinusoidally varying in the direction of propagation. In light of the weak variation of the materials properties, the perturbation method of multiple scales is utilized to analyze the modal interaction which occurs upon the satisfaction of certain resonant conditions. The derived coupled-mode equations together with relevant boundary conditions at the ends of the inhomogeneous section form a two-point boundary value problem, which is solved numerically. The power reflection coefficient is then calculated to present the reflection characteristics of the plate.