A hybrid Green function method in time domain was applied for simulating the motions of floating body in waves. The fluid filed was decomposed into inner and outer domain by an imaginary control surface; the Rankine source method was applied in the inner domain while the transient Green function method was used in the outer domain. Two initial boundary value problems were solved by the continuity condition on control surface. The corresponding numerical codes were developed and the retard functions, wave exciting forces and motions in waves for a cylindrical platform and S175 containership were presented and verified. The comparison between numerical results, experimental data and frequency results were in good agreement, which shows that the present method is efficient and suitable for the hydrodynamic problem with or without forward speed. The good numerical stability is proved by solving divergence problem of ship with flare.