Surveys of filefish spawning ground and in combination with the strength anal the position variation of the eddy off Diavyu Tsland in Spring (April) from 19$1 to 1984 were carried out. Marine conditions such as temperature,salinity, density б_t specific volume anomaly 10⁵δ and Geostrophic current, were analysed in order to find out the reason of the formation of spawning ground and the variation of catches，and It is expected to provide a basis for fishing forecast, The principal results are as fellows: 1.There exists a cyclonic eddy in the sea area at the northeast of Diaeyu Island(26°-27°N, 124°-125°E)，that is the area of Kuroshio and its branched region.The velocity ef the upwelling in the center of the eddy is in the order of about 10^-4cm/s, and around it is downwelling area. Besides rotation, the Eddy moves horizontally towards northeast，and the velocity is about 0.8km a day. On the northern and western edges of the eddy，the velocity is comparatively slow, where is the passing and spawning greunds of filefiish. 2.In spring, the spawning grounds of filefish generally concentrated in the near bottom stratum of the eddy region and its edge off Diaoyu Island (26°N section ),of which the seatva#er temperature was 17-18℃, the salinity was 3.4.6-34.8‰ and the specific volume anomaly 10⁵δ of 270-290. 3.The eddy characteristics off Diaoyu Island in 1982 and 1983 were obviously different that the yield fluctuation of these two years was influenced to a certain extent. 4.The strength and the position of the eddy off Diaoyu Tsland ( 26°N section )have variation each year during 1981-1984. Supposed. the specific volume anomaly 10⁵δ on the bottom of the eddy is taken as an index to n3easure the strength of the ocean water, the correlational coefficient between it and the filefish production of Shanghai a ud Zhoushan Marine Fishing Compaxiies in April and May could reach 0.9i3，and that between the index and the total annual production was 0.812. So this hydrographio factor can be offered as an index for fishing prealiction. 5.Tha larvae ef filefish basically drift along the current around the eddy towards northeast gradually.