Tidal effects on the Yellow Sea circulation and ecosystem variables have been investigated using a physics-ecosystem coupled model. The results of model experiment for two cases of including and excluding tide, were compared. In the sectional view along the 36°N, cold water appears in the eastern side of the Yellow Sea in winter for both cases. In case of including tide, cold water moves gradually toward the central bottom of the Yellow Sea and get settled there in summer, which is similar to observations. In the case of excluding tide, however, YSBCW appears and disappears in the eastern side of the Yellow Sea, and the stratification is weaker than that in the case with tide. The responses of ecosystem variables along the 36°N section were also discussed for the two cases. In the experiment including tide, high concentration of phyto- and zooplankton appears in the eastern part and less high one in the western bottom of the Yellow Sea and lowvalues in the upper layer of the western part in summer.