Abstract: This paper presents the results of investigation on the plankton of Qinghe reservoir during the six years: 1970, 1973—74 and 1977—79, The reservoir is located in Liaoning Province, Northeastern China, with an submerged area of 46 km and a mean depth of about 10 m (maximum depth 30—33 m).The standing crop of phytoplankton in Qinghe reservoir during the surveying period varied from 1.05 to 24.41 mg/l, among which Bacilladophyta was the most predominant group, being 58.6% of the total biomass. Next came Pyrophyta (25.9%), Cyanophyta (8.0%), Chlorophyta (3.5%), Chrysophyta (2.8%) and Euglenophyta (only 1.0%).The average biomass of zooplankton was 1.95 (0.34—10.51) rag/l, in which the copepoda presented 44.1%, the Cladocera—40% and the Rotifera and Protozoa—only 15.9%.About 40 dominant or most common forms occur in the reservoir. The most important species of them are: Melosira granulata, Cyclotella comta, Cryptomonas sp, Ceratium hirundinella, Bosmina coregoni, Daphnia longispina, Cyclopida and Polyarthra trigla.In general, the biomass of phytoplankton and zooplankton is higher at the upper and middle reaches than that at the lower reach. The phytoplankton is maximum in autumn and the zooplankton is maximum in summer, but in 1978 the phytoplankton maximum shifted to Summer owing to an extraordinary low water level.In this paper the distribution and fluctuations of the plankton and the potential fish productivity of Qinghe reservoir are also discussed.