A seamless coastal gravimetric quasi-geoid model was computed using a combination of heterogeneous gravity data. A comparison to the precise GNSS/leveling derived height anomalies, accurately determined the discrepancy of the 1985 national height datum with respect to the gravimetric quasi-geoid. Based on the numerical results, the discrepancy of the 1985 national height datum with respect to the gravimetric quasi-geoid with W0
defined by IERS2010 standard is 30.4±1.0 cm. After transmitting the 1985 national height datum to Hainan Island through the Qiongzhou Strait in 1980s, the regional height datum of Hainan Island showed no significant bias at the 1 cm accuracy level. The standard deviation of the differences between the GNSS/leveling derived height anomalies and the computed quasi-geoid model was 4 cm. The quasi-geoid is seamless across the borders of the 13 provinces and cities. Research findings show that during the last ten years, land subsidence is extensive over most areas of Tianjin except for its northwest corner, where the land subsidence over southeast area reaches up to 7 cm. The land subsidence of Shanghai is about 7 cm, and there are various degrees of land subsidence in some parts of Zhejiang, Jiangsu and Fujian as well.