Observed relative sea level (RSL) changes in East Asia Seas are studied with the help of our latest 3D glacial isostatic adjustment(GIA) model, which employs the finite element method to simulate RSL changes since the Last Glacial Maximum(LGM). From the temporal and spatial variation of predicted RSL, it is shown that the early rise of sea levels after LGM is mainly influenced by the addition of melt-water into the oceans while the later RSL changes are strongly affected by mantle flow, ocean loading and crustal adjustment. Thus, the RSL results show obvious regional changes for each epoch. The uncertainty of modeled RSL is mostly attributed to the differences in the ice models used, and its magnitude is found to be comparable to the measurement error.