The present paper is the result about the ecological stutides on the zooplankton in the Changjiang River Estuary(121°31'--124°E,30°45′N-32°00′N) The net samples were collected eleven times at thirty-forty one permanent stations from August 1985-july 1986. T'he total biomass of zooplankton is highest in Changjiang River Estuary. In general,it reaches a maximum in July and reduces to a minimum in April. This type of seasonal variation was essentially the same as observed in the Changjiang River, Estuary in 1958-1959, 1960 1961,1972,1973,1985-1986. The distribution zone of high biomass of zooplankton was located at the mixed place of different water masses during the period of maximum river runoff.When runoff from the river is low, the distribution zone of high biomass of zooplankton was located at the coastal water of the Changjiang River Estuary. A total about 169 species of zooplankton and 10 groups of plankton larvae were found in the investigated area. The zooplankton of the area is dominated by Copepoda and Chaetognatha, the important species of which are Calanus sinicus, Labidocer euchaeta,Acartia pacifica,Tortanus vermiculus, Schmackeria poplesia, Sagitta enflata and Sagitta nagae. Based on the relation of biological characteristic and distribution of species with the current system, the zooplankton may be divided into four ecological groups: (1)freshwater species; (2)semi-saline estuarine species, (3)low salinity neritic species,(4) warm water species.