Abstract There are two different schools of thought with regard to the origin of the Tsushima Warm Current. One school of thought believes that it comes from the Taiwan Strait, while the other believes that it enters the East China Sea from the Kuroshio region southwest of Kyushu, Japan, crossing the steep shelf slope. Using the seasonally averaged distributions of the wind (30-year mean of Comprehensive Ocean Atmosphere Data Set) and density (data from 1961 to 1990 supplied by Japan Oceanographic Data Center) in the East China and Yellow Seas, we determine the volume transport distribution diagnostically through a numerical model in which we solve the vorticity equation of the vertically averaged flow. Then, we try to identify the origin of the volume transport of the Tsushima Warm Current and its seasonality. The results except for the autumn indicate the existence of the so-called Taiwan–Tsushima Warm Current System (Fang et al., 1991), i.e. a continuity of the volume transport between the Taiwan and Tsushima/Korea Straits. However, this current system breaks down in the autumn. According to this study, about 66% of the volume transport of the Tsushima Warm Current comes directly from the Kuroshio region in autumn, crossing the shelf edge of the East China Sea.