In the sound propagation in shallow water, the influence of an internal wave is worthy of attention. We investigated the influence of the shallow water internal wave on the sound propagation on the continental shelf. The internal wave was assumed to be 100 m wide, with an amplitude of 22.5 m. The relation between the position of the internal wave and the turning ray was examined at 50 m in sound source depth in the thermocline. Because the turning position and the internal wave overlap, a strong scattering is caused at the rear and underside of the internal wave. Moreover, the width of the influence to the turning position is ±400 m regardless of the position of the internal wave. We also determined that the influence increases according to the extent of the internal wave width.