In order to further improve the computation efficiency of seakeeping prediction for the ships with forward speed, the symmetry property was introduced into the calculations of velocity potentials in the 3-D translatingpulsating source Green function method. Based on the Green function′s symmetry, the specific measures were put forward to evaluate the ship hydrodynamics. By the symmetrical magnitude of source point to field point, the integral symmetry expressions of normal derivative of harmonic function at the symmetric line and surface elements were derived and obtained. The symmetrical characteristics were applied to simplify the matrix of coefficient in the boundary integral equation. A theoretical method with high efficiency was presented for the seakeeping performance of 3-D ship advancing in waves. Numerical results and example analysis show that the symmetry property of translatingpulsating source Green function is available for the minimization of computation and memory amount and is proved effective in the numerical calculations of wave exciting forces, motion responses and free-surface waveform for the advancing ship in waves. It is expected to extend the symmetrical characteristics of translating-pulsating source Green function to the hydrodynamic analyses of interacting two ships or complex ship form in frequency domain.