Abstract: Studies on the seasonal characteristics of fish communities structure and diversity are conducted, based on data from bottom trawl surveys in 4 seasons of 2000 in the East China Sea and the Huanghai Sea.Around all survey areas there were totally 8 dominant species in 4 seasons, which were Trichiurus japonicus, Pseudosciaena polyactis, Setipinnataty, Acropoma japonicum, Apogonlineatus, Engraulis japonicus, Champsodon capensis, Psenopsisanomala.Trichiurus japonicus and Pseudosciaena polyact is were dominant around 4 seasons, and the other species were only dominant partly in 4 seasons.During the 4 seasons the fishs movement in the nor h of the Huanghai Sea was the strongest, in the middle of East China Sea the weakest and in the north of East China Sea middle.The biodiversity indexes of species richness index(D), Shannon Wiener index(H') shown the same trend:there were not apparent differences among three areas in spring and summer, but in autumn and winter the indexes of the south of yellow sea became lower, and that of the north and the middle of East China Sea became higher.Species evenness index (J') shown no apparent differences among 4 seasons and 3 areas.By comparison it was found that during summer and autumn the south fish communities are in the trend of migrating to the north, on the other hand the north fish communities are in the trend of migrating to the south during spring and winter.