Based on the hydrographic data and moored current meter records during the summer cruise (June 11-July 18, 1984) and winter cruise (December 25, 1984-January 31, 1985), a diagnostic calculation of three dimensional ocean circulation in the survey area was performed for each cruise. The results show (i) Taiwan Warm Current was the dominant feature in the survey area during both cruises. In summer the Taiwan Warm Current was composed of two current systems, namely, the offshore branch derived mainly from the Kuroshio northeast of Taiwan and the inshore branch originated mainly from the Taiwan Strait. In winter, both branches seemed to have originated from the Kuroshio northeast of Taiwan, but the contribution from water through the Taiwan Strait was also possible for the inshore branch, (ii) In winter the coastal current flowed southward to the west of a strong coastal front, while the Taiwan Warm Current flowed northward to the east of the front, (iii) Upwelling occurred near Zhejiang coast in summer and Based on the hydrographic data and moored current meter records during the summer cruise (June 11-July 18, 1984) and winter cruise (December 25, 1984-January 31, 1985), a diagnostic calculation of three dimensional ocean circulation in the survey area was performed for each cruise. The results show (i) Taiwan Warm Current was the dominant feature in the survey area during both cruises. northeast of Taiwan and the inshore branch originated mainly from the Taiwan Strait. In winter, both branches seemed to have originated from the Kuroshio northeast of Taiwan, but the contribution from water through the Taiwan Strait was also possible for the inshore branch, (ii) In winter the coastal current flowed southward to the west of a strong coastal front, while the Taiwan Warm Current flowed northward to the east of the front, (iii) Upweusing occurred near Zhejiang c oast in summer and