Tidal waves in the Easl China Sea are simulated numetically with POM (Princeton Ocean Model) model for normal mcan sea level, 30cm higher, 60cm higher, and 100cm higher, respcctively, and the simulated rsult is compared with the harmonic analysis reult of hourly sea level data from 19 fide ganges for more than 19 years. It is indicated that the long-term mean sea level variation affects notably tidal waves in this region. Generally, the tidal amplitude increases when the mean sea level rises, but this relationship may be inverse for some sea areas. The maximal variation of tidal amplitude takes place in the zones near the Fujian coast and the Zhejiang coast, rather than the shallowest Bohai Sea. The maximum increase of M2 amplitude can excced about 15cm corressponding to the 60cm rise of the mean sea level along the Fujian coast. The other ragions with large variations of tidal amplitude are those along the Jiangsu coast, the south-east coast of Shandong, and the south-east coast of Dalian. The propagation of tidal waves is also related to mean sea level vatiation, and the tidal phase-lag decreases generally when the mean sea level rises. Almost all the ragions where the tidal phase-lag increases with rising mean sea level are close to amphidromic points, meanwhile the spatial area of such regions is very small. Because the influence of mean sea level variation upon tidal waves is spatially marked, such spatial effect should be considered in calculation of the tidal characteristic value and engineering water level. In the region where the amplitudes of the major tidal constituents increase, the probable maximum high water leval becomes higher, the probable maximum low water level becomes lower, and both design water level andcheck water level increase obviously. For example, the design water level at Xiamen increases by 13.5cm due to the variation of tidal waves when the mean sea level rises 60cm, the total increase of design water level being 73.5cm.