Abstract: A numerical model of the Northwest Pacific is developed to study tidal system and tidal level changes due to mean-sea-level rise in marginal seas near China. The results show that after mean-sea-level rise, phase lags are increased to the east and decreased to the west of amphidromic point. The amplitude is enhanced to the north and diminished to the south of amphidromic point. Due to mean-sea-level rises, the mean tidal range is enlarged in the Liaodong Bay, the upper reaches of Bohai Bay, seas east of Liaodong Peninsula, coast of Haizhou Bay to the south of Shandong province, the north coast of Jiangsu province, the Taiwan Strait to the east of Zhejiang province, and the South China Sea. The maximum range is 0.40 m after mean-sea-level rise 0.90m. The mean tidal range is reduced in estuary of Yangtze River, Hangzhou Bay to Tsushima Strait, the west coast of Korea, and Laizhou Bay. With the increase of sea level rise, tidal range varies with relatively stable rate in the Bohai Sea, Taiwan Strait, and it with fluctuation in the Yellow Sea, East China Sea and South China Sea. Variation of mean high water level is in accord with tidal range. It uplifts more over than the mean-sea-level in areas where tidal range raises. That means the risk would increase of coastal areas to protect storm surge and other marine disasters.