Abstract: A time domain finite volume method (TDFVM) is applied to analyze the transient response and natural characteristics of structural-acoustic coupling problems in an enclosed cavity based on wave theory. In present method, elastic dynamic equations and acoustic equation in heterogeneous medium are solved in solid domains and fluid domains respectively. The structural-acoustic coupling is implemented according to normal components of particle velocity continuity condition and normal traction equilibrium condition at the interface. The accuracy and precision of TDFVM are validated through numerical examples. Then TDFVM is used to analyze the influence of water depth on the sound and vibration characteristics and the natural characteristics of a structural-acoustic coupling system. The numerical results show that the increase of water depth leads to a stronger coupling between the water and structure and the decrease of natural frequencies of coupling system, while the decrease of air cavity leads to the increase of part of natural frequencies of acoustic cavity. The computational cost and memory of this method are small and it is applicable to structural-acoustic coupling problems in heterogeneous fluid.