Based on a three-dimensional primitive equation dynamic numerical mod-el,the general circulation in the East China Sea and the Yellow Sea is studied with a O.25°×0.25°horizontal grid and a realistic bottom topography.As the first step,we con-sider the tidel current and Kuroshio(Japan current).The main results are:1)the modeltidal harmonic constants agree surprisingly well with the observations at the 81 coastlinestations in this area.The average amplitude difference is 1.7cm and the average phase dif-ference is 5.2°for the diurnal component,and those for the semi-diurnal tide 4.1 cm and3.7 °2)the path of the Kuroshio agrees with long—term observations; 3)after enteringthe studied area, a branch of the Kuroshio enters the East China Sea.This pattern agreeswith the nation-wide comprehensive ocean investigations; 4)a branch of the Kuroshiogoes northward and forms the Tsushima warm current,and the origin of Tsushima warmcurrent is multi-source.In the Tsushima Strait,the warm current goes into the Sea o Based on a three-dimensional primitive equation dynamic numerical mod-el, the general circulation in the East China Sea and the Yellow Sea is studied with a 0.25 ° × 0.25 ° horizontal grid and a realistic bottom-topography. As the first step, we con-sider the tidel current and Kuroshio (Japan current). The main results are: 1) the modeltidal harmonic constants agree surprisingly well with the observations at the 81 coastlinestations in this area. The average amplitude difference is 1.7cm and the average phase dif-ference is 5.2 ° for the diurnal component, and those for the semi-diurnal tide 4.1 cm and 3.7 ° 2) the path of the Kuroshio agrees with long-term observations; 3) after entering the studied area, a branch of the Kuroshio enters the East China Sea. This pattern agrees with the nation-wide comprehensive ocean investigations; 4) a branch of the Kuroshiogoes northward and forms the Tsushima warm current, and the origin of Tsushima warm current is multi-source. The Tsushima Strait, the warm current goes into the sea o