The national benchmarks on islands were mostly established by trigonometric leveling in Korea. This method results in inaccuracy, which is a serious problem in Geoga Grand Bridge construction work that tried to link the mainland and the islands. The Geoga Grand Bridge (Pusan-Geoje fixed link project) was selected as the study area, a huge construction work in Korea that will connect the mainland (Pusan) and an island (Geoje island). However, the orthometric heights issued at benchmarks (JINH and GOEJ) were not consistent, because they did not refer to the same zero point, which would make the linking of the sections problematic. This paper introduces the precise local geoid as a vertical datum for the construction area in order to establish a consistent height system. To determine the precise local geoid for the construction area, we firstly developed a precise gravimetric geoid for Korea and its adjoining seas as a whole. This gravimetric geoid was developed by use of all available gravity data, including surface and satellite data on land and on the ocean. The gravimetric geoid was computed by spherical fast fourier transform with modified Stokes' kernels. The remove-restore technique was used to eliminate the terrain effects by use of the RTM reduction and to determine the residual geoid by combining the GGM02S/EGM96 geopotential model, free-air gravity anomalies and high-resolution DEM data. Finally, the gravimetric model was fitted to the geoid heights obtained from GPS and tide observations (N_(GPS/Tide)) by least square collocation, to provide the final GPS-consistent local precise geoid model. The post-fit error (std. dev.) of the final geoid to the N_(GPS/Tide) derived from GPS and tide observations was ±2.2 cm for the construction area. We solved the height inconsistency problem by calculating the orthometric height of the benchmarks and the control points using the final geoid model. Also, the highly accurate orthometric height was estimated through the GPS/leveling technique by applying the developed local precise geoid. Therefore, the precise local geoid is expected to improve the quality of the construction procedure of the Geoga Grand Bridge.