The dormant egg bank in sediments has been regarded as a pool of species diversity and genetic information of freshwater Cladocera.Hatchings from the sediments strongly and directly affect the abundance and genetic structure of active population of Cladocera.In the present study,we sampled the active population in water column and picked up dormant eggs of Daphnia galeata in the top 10 cm of the sediment in Liuxihe Reservoir.We used cytochrome C oxidase subunit I gene to reveal the haplotype diversi-ty and genetic differentiation of active and dormant populations of Daphnia galeata in the reservoir.Our results showed the dormant population had higher haplotype diversity and nucleotide diversity than the active population.The haplotype diversity and nucleotide diversity were 0.562 and 0.00104 for the initial active population,0.726 and 0.00331 for the end active population,and 0.815 and 0.00761 for the dormant population,respectively.The coalescent calculation suggested that there was a bi-directional gene flow be-tween the active and dormant populations:the effective migration rate was 490.9 from active population to dormant population and 527.5 from dormant population to active population.We did not find hidden or subspecies differentiation in the dormant population and the active population by means of a Bayesian system tree.No significant genetic differentiation between the dormant population and the active population suggested that the genetic diversity of the active population was contributed by the dormant population.Therefore,the dormant population reflects the total genetic diversity of populations in the reservoir.The gene flow between the dor-mant and active populations was related to the hatching of dormant eggs rather than the size of the dormant eggs.