This paper discuss the behavior of ship structural panels subjected to acoustic excitation. In order to provide a clear understanding of the phenomenon of course of transmission of sound by a flexible panel, two dimensional sound-elastic interaction vibration problem has been examined. We have assumed two vibration models on a panel in an infinity large rigid baffle. The one is a Timoshenko model, the other is a two dimensional elastic model. We have introduced the exact solution of Timoshenko model and have formulated the coupled vibration of sound-elastic interaction model using the boundary element method. Comparing the sound transmission loss between the two models, we have shown that the principal element of the sound transmission is caused by out of plane vibration of panel and the transmission by in plane vibration can be neglected.