The tide phenomena in the marginal seas have attracted many people’s attention since ancient time. Systematical studies based on modern theories began early in the present century. In 1930’s, Ogura published cotidal charts for the Eastern China Sea which were considered as standard for many decades. The sea level data for the South China Sea were quite poor at that time compared with the available data in the Eastern China Sea. The cotidal charts produced by Dietrich (1944, see Defant 1961) were not accurate. The tide phenomena in the marginal seas have attracted many people’s attention since ancient time. Systematical studies based on modern theories began early in the present century. In 1930’s, Ogura published cotidal charts for the Eastern China Sea which were considered as standard for many decades. The sea level data for the South China Sea were quite poor at that time compared with the available data in the Eastern China Sea. The cotidal charts produced by Dietrich (1944, see Defant 1961) were not accurate.