Abstract: Objective: In order to solve the problem of global vertical datum unification, this paper unifies the local vertical datum into the global vertical datum based on the geodetic boundary value problem together with EIGEN-6C4 Earth gravity field model, GNSS/level data and gravity anomaly data. Methods: In order to improve the omission error of the earth's gravity field model, the space-domian method and the remaining terrain model are used to convert the remaining terrain into gravity field signals, and then the gravity field information of the whole band is obtained based on the removal-recovery method. Results: Experiments show that the RTM terrain effect reaches the decimeter level in both the US region and the Chinese region. Therefore, in order to improve the modeling accuracy of the regional gravity geoid, especially in areas with large terrain fluctuations, the influence of the remaining terrain should be considered. Conclusions: Finally, the gravity potentials of China's 1985 national vertical datum and NAVD88 elevation datum were determined based on the space-domian method and the geodetic boundary value problem, respectively, 62636852.749m²s^-2 and 62636852.186m²s^-2.