Abstract: For the coastal zone, the multi-source gravity data co-exist and terrain features are diversity, through theoretical analysis and a spreadsheet, some issues in quasi-geoid determination with cm-level precision were discussed, and draw some useful conclusions. Taking into account Molodensky first-order contribution to the height anomaly about 10 ~ 30cm in China's coastal region, refined gravity quasi-geoid should be in the Molodensky frame. Fine topographic effect processing is a fundamental way to handle multi-source gravity data. The algorithm for topography effect, mass compensation and helmert condensation for any height, any type gravity field parameters in earth outer space can be unified. The effect of the inconsistent geodetic reference to the gravity data processing vary with the data processing algorithm. in multi-source gravity data processing procedure such influence can be unpredictable. The terrain Helmert condensation can be introduced to Molodensky framework with any type of gravity data