This paper discusses the distribution and abundance of the Cladocera and Cumacea collected in Changjiang Estuary and adjacent waters(29°00'-32°00'N and 122°00'-123°30'E)from May 2002 to March 2003.The abundance of Cumacea peaked in summer at 0.59 ind./m³ and the lowest abundance was in spring at 0.05 ind./m³.The seasonal abundance of Cumacea was influenced by sea surface temperature while the horizontal abundance was influenced by the surface salinity.Totally,four species,i.e.,Diastylis tricincta,Bodotria ovalis,Dimorphostylis asiatica,Iphinoe tenera were recorded,among which D.tricincta was presented in the four seasons with the dominance 0.04,0.03,0.04 and 0.06,respectively;B.ovalis was observed in summer,autumn and winter with the dominance 0.11,0.00 and 1.07,both D.asiatica and I.tenera were observed in autumn with the dominance 0.17 and 0.002 separately.Two Cladocera species,Evadne tergestina and Penilia avirostris,was only recorded in summer with abundance of 32.13 ind./m³ and 43.82 ind./m³.The species of pelagic Cladocera and Cumacea adapted to the brackish water environment so that their distribution was closely related to the Changjiang Dilute Waters.