Abstract: Based on the data acquisitioned in the 4 times marine habitat monitorings carried out from December 2003 to September 2004 in Daya Bay, the community composition and ecological groups of planktonic Copepods as well as its abundance distribution and seasonal changes in the sea were studies. Among 54 species identified, Acartia erythraea, Eucalanus subcrassus, Canthocalanus pauper and Temora turbinate were dominant ones in the survey region. The species and abundance of Copepods in the area were highest in summer and lowest in spring. Through this survey we could got such conclusion. Among zooplankton, the species of Copepods was the most, but its abundance was fewer than that of Chaetognatha and Cladocera. The abundance fastigium of Copepods appeared in Summer and Autumn, and Acartia erythraea was the utter dominant specie. The Copepods could be divided into three ecological groups such as high temperature and high salinity group, neritic low salinity group and eurythermy and eurysalinity group. The fauna of planktonic Copepods in Daya Bay belong to Indo-West-Pacific-tropic-fringe Region.