Abstract: Based on postprocessor GPS PPK technology,we carried out the research on long-distance tide ob-servation and extraction,the determination of vertical datum and the construction of vertical-datum transfor-mation model.A model for calculating a height series for instantaneous water surface was researched,mean-while,the best cut-off periods for tidal extraction for anchored and on-the-fly status are proposed.Finally,based on long-term anchor PPK and tide-gauge tidal levels for different situations,a determination ofMSL and chart datum as well as the models for calculating their geodetic heights were investigated andproposed.A method to establish a seamless chart datum geodetic height model is presented.An testproject showed that the accuracy of GPS tide level reference to chart datum measurement method aspresented in paper can be better than 10cm when the GPS baseline is less than 100km.