Fluctuations in the ocean are closely related with the underwater acoustic propagation. Internal waves are generated by fluctuation of isopycnal layer in the upper part of the stratified ocean, which are propagated from offshore to coastal area. Physical characteristics of the internal waves existed in the East Sea were derived from the five field experimental data and the ocean monitoring buoy nearshore the mid-east coast of Korea. The dominant periods are appeared in the near-inertial period about $17{sim}20hours$ and the short period about a few minutes. The wavelengths of them are $10{sim}50km$ and $300{sim}1000m$, and the phase speeds are $20{sim}100cm/s$ and $30{sim}70cm/s$, respectively The maximum amplitudes are about $20{sim}25m$. Under the environment of short depression internal wave propagation, the variations of transmission loss field were investigated using an range-dependent acoustic transmission loss model(RAM). The result shows that the large irregular variations of transmission loss caused by progressing the internal wave from offshore toward coast.