We develop a numerical method to investigate the dynamic response of cargo ship in waves. The cargo ship is simplified as a structural system of three-dimensional frame finite elements. The element mass matrix is calculated by the lumped mass matrix method. The two-dimensional hydrodynamic forces acting on the transverse section of hull elements are evaluated by the Strip Method. The Newmark-beta method is applied to solve the dynamic equation. A 9,688DWT cargo ship with unbalanced loading cargo of steel coil is taken as a numerical example to be analyzed. The study emphasis is placed on the influence of the cargo loading conditions on the dynamic response of the cargo ship in waves.