The authors conducted a field investigation in Hengqin Island Sea in May 2008,and studied the chlorophyll a content, primary production,zooplankton and phytoplankton.Some parameters such as composition,community structure,abundance and biomass of phytoplankton and zooplankton were analyzed.The results showed that the average chlorophyll a content and primary production was 5.27 mg·m^-3 and 123.56 mg·m^-2·d^-1,respectively.111 phytoplankton species were identified.Phytoplankton communities were dominated by Bacillariophyta and the absolute dominant species was Skeletonema costatum.The main ecological group of phytoplankton was nearshore group;the average cell density of phytoplankton was 6 832.75×10⁴ cell·m^-3.41 zooplankton species were identified,among which the absolute dominant species is Acartiella sinensis.The main ecological group of zooplankton was warm water nearshore group.The average abundance and biomass of zooplankton were 742.25 ind·m^-3 and 131.12 mg·m^-3 respectively;the average diversity index and evenness of zooplankton were 2.54 and 0.67,respectively.