A preliminary numerical model of the buoyant drum by wave action is presented, which is based on The Finite Boundary Element Method of the source distribution. A series formula of Green’s function is used for the derivation of the model. In the paper the calculated results of the examples for a sphere and a buoyant drum are close to the data in some references. A subject of great interest to ocean engineers is the response a floating body suffers in ocean waves. In this paper, the oscilatory motion of a buoyant drum is analysed and a calculating method is presented. Applying this calculating method, the hydrodynamic coefficient for any kind of floating bodies can be obtained. A preliminary numerical model of the buoyant drum by wave action is presented, which is based on The Finite Boundary Element Method of the source distribution. A series formula of Green’s function is used for the derivation of the model. In the paper the calculated results of the examples for a sphere and a buoyant drum are close to the data in some references. A subject of great interest to ocean engineers is the response a floating body suffers in ocean waves. In this paper, the oscilatory motion of a buoyant drum is analysed and a calculating method is presented. Applying this calculating method, the hydrodynamic coefficient for any kind of floating bodies can be obtained.