The relationship between cyclops and microcystis aeruginosa had been studied.The static test was divided into 5 groups in concordance with different proportion of populations and studied with periods of 13 days.The way of counting includes micro-metering and numbering.The results show that when the cyclops density is 100/L and the microcystis aeruginosa density is 108/mL,they inhibite each other strikingly.When the microcystis aeruginosa density is reduced to 107/mL,their inhibitory action is also obvious.And then if the cyclops density is reduced to 50/L,the inhibitory action becomes undistinguishable.So there is a proportional relationship between the inhibition intensity and their density.This study provides a new idea and theoretical basis for water bloom and cyclops overpopulated.