Abstract: On the basis of the data from four seasonal oceanog raphic censuses in the East China Sea (23.30~33 N, 118.30~128 E) in 1997~2000, the paper studies on adaptation and ecotype of Ostracoda in the East China Sea through curve fitting, forming mathematical model, calculating optimal temperature and salinity, consulting geographic distribution based on synchronous data of abundance and environmental factors.The results show that in the dominant species, Euconchoecia maimai, E Chierchiae, Cypridina dentate, E aculeate and E elongata are off shore subtropical water species with wide distribution.They can occur in north off shore waters because warm currents may take them from low latitude areas to there during winter and spring.The mathematical analyses show that optimal temperatures of Paraconchoecia decipiens, P echinata, P spinifera, Conchoecia magna, P oblonga and Porroecia porrect are over 25, and their optimal salinity over 34, mainly distributing in waters of Kuroshio, the Taiwan Warm Current and the Taiwan Strait, which all make the species qualified as oceanic tropical water species.Though Pseudoconchoecia concentrica and Conchoecia sp have low optimal temperature, characters of their geographic distribution ascribe the former to of fshore subtropical water species and the latter to temperate warm water species.The optimal temperatures of the rest species are between 15 and 20.Though most of their optimal salinity is over 34, these species can widely distribute in areas from the East China Sea to the Nansha archipelago with not high density and their distribution are related with warm currents so that they can be defined as offshore subtropical water species.