In this paper, the author deserides the mean sea level of the coastar areas in China as higher in the south and lower in the north and analyzes the affect of the sea topography, surface runoff and tendency of rising in the south and dropping in the north upon the mean sea level.

The harmonous constants of 11 tidal constituents,mean sea level,and characteristic tidal level were obtained and validated.

The tidal level data from 21 tidal stations in radial sand ridge sea area of Jiangsu Province are analyzed by use of G-Godin s tidal harmonic analysis and prediction programs revised by M Foreman,and the harmonic constants of 11 constituents and corresponding mean sea level are obtained.

In this paper, the especially big mineral ore transfer wharf project at Majishan of Shengsi Islands was taken as an example, through relevant analysis and differential calculation, the mean sea level and its relation to the datum levels at Majishan were ascertained on the basis of collection, checking and calculation of the long term data in tidal stations.