This paper first develops the approaches to determine the geopotential of the local mean sea level, and then investigates the offset of the 1985 vertical datum surface defined by the mean sea level of Yellow Sea at the Dagang Tide Gauge in Qingdao city using the developed approaches and GPS/leveling data. It shows that the geopotential of the local mean sea level at the tide gauge is equal to 62 636 853.5±0.2 m2·s−2 and that the 1985 vertical datum surface is 24.6±5.4 cm above the geoid realized by the geopotential W0=62 636 856.0±0.5 m2·s−2.