The Princeton Ocean model was used to simulate the circulation in the Huanghai Sea and East China Sea and its annual cycle showing that: (1)A weak countercurrent exists on the left side of the Kuroshio. The countercurrent separates from the main stream of the Kuroshio around 30°N, 128°E, flows southwestward along isobaths, meets with the offshore branch of the Taiwan Warm Current around 28°N, 124°E, then returns back and joins the main stream, thus forming a cyclonic circulation. (2) The Taiwan Warm Current has an inshore branch and an offshore branch. Only in summer, the inshore branch can reach to about 30°N, where separates into two branches; one flows northward Changjiang River mouth, the other flows eastward, to be one of the sources of the Tsushima Warm Current. (3) The Tsushima Warm Current has multiple-sources. (4) In summer, Huanghai Sea Warm Current does not enter the southern Huanghai Sea. It mainly origins from the middle shelf flow in seasons other than autumn, in summer, it seemingly comes from the extension of the inshore branch of the Taiwan Warm Current. (5) The Eddy in the northern East China Sea exists all year round, with a closing cyclonical circulation in winter and summer. The seasonal variation of the eddy is influenced by the components of the cyclonical circulation, such as the Huanghai Sea Warm Current and middle shelf flow.