In this study, we at first employ a simplified 1-D layered spherical Earth model to compute the co- and post-seismic vertical displacement and geoid change on the seafloor surface due to the 2004 Sumatra earthquake. We then use a pseudo-spectral algorithm to iteratively solve SLE and obtain RSL and geoid changes of long wavelength(>90 km). Results show that the contribution of redistributed seawater mass on RSL is secondary, which can be neglected when we focus on the long wavelength RSL. The effect of geoid change due to the redistribution of seawater mass mainly stems from the self-gravitation of seawater disturbed by earthquakes, while the contribution from elastic load response is an order of magnitude smaller. In addition, we examine two approximate methods of ocean water effect—solving SLE with a uniform ocean covering and Bouguer layer approximation. Comparison results show that both two methods can effectively estimate the co- and post-seismic ocean water effect of the 2004 Sumatra earthquake. The seawater mass effect estimated by Bouguer correction formular is in better agreement with that obtained from solving SLE with a realistic ocean.