In this study, we develop an immersed boundary method - volume of fluid (IBM-VOF) two-phase flow solver to simulate two-phase flow problem contains solid boundaries and free surface and use it to solve the typical problems for floating marine structures. In the solver, the IBM method is adapted to solve the problems of the moving marine structures and the VOF method for solving the problems of a free surface flow. The free surface at the fluid is considered as the mixed fluid of sea water and air in the solver. Base on this IBM-VOF two-phase flow model, hydrodynamic analysis of a floating marine structure with forced heave motion is done, and hydrodynamic force coefficients are computed. In this case, we firstly calculate the forces of the floating marine structure under different frequencies, and then we get added mass and added damping through fitting the data of the forces by the least square method. The results obtained from the present model are compared, which verified the reliability and accuracy of this numerical model.