Abstract: This paper reports the results of estimations of population dynamics and production of Daphnia hyalina and D. carinata ssp. in lake Donghu in Wuhan carried out during 1980—1982. The ecological factors affecting the population dynamics and production of these two species are analyzed. Daphnia hyalina and D. carinata ssp. are considered to be the most dominant Cladoeerans in the lake. The two species prevailed alternately. In general, the population density of Daphnia hyalina expressed as number of individuals/1 shows a maximum in spring or winter, But, the occurrence of summer or autumn maximum was recorded for D. carinatta ssp. On the basis of data in 1980—1982 at station Ⅱ, the average annual abundance was 28.43(17.59—38.50) ind./1 for D. hyalina and 4.64(3.79—5.31) ind./l for D. carinata ssp.The instantaneous birth rate (b) was nearly always in greater than the instantaneous growth rate (r); the instantaneous death rate (d) in general paralleled changes in birth (b).Similarily, the mean annual biomass of Daphnia hyalina was 0.218 (0.175—0.315)mg dry weight/1; 0.046(0.039—0.060)mg dry weight/1 for D. carinata ssp.The average annual production of Daphnia hyalina was 9.181(4.877—13.428)mg dry weight/1./year, 3.417(2.752—3.829)mg dry weight/1./year for D. carinata ssp. The average annual P/B ratio was 42.38 (27.76—56.7) for D. hyalina and 77.04(61.24—99.74) for D. carinata ssp..