Abstract: To investigate the effects of cadmium (Cd²⁺) on the feeding capacity and its mechanism of water flea, Daphnia magna, three experimental groups with different Cd²⁺ concentrations (0.01 mg/L, 0.05 mg/L and 0.09 mg/L) and one control group were set up in this study, and these groups were exposed for 24h and 48h, respectively. The effects of Cd²⁺ levels on the feeding and filtration rate, tissues accumulation of Cd²⁺, total antioxidant capacity (T-AOC), contents of malonyldialdehyde (MDA), and the activities of acetylcholine esterase (AChE) in D. magna were analyzed. The results showed that (1) the feeding and filtration rates of D. magna decreased with increasing Cd²⁺ concentrations. Especially, when the D. magna was exposed to 0.09 mg/L Cd²⁺ for 48h, the feeding and filtration rates dropped dramatically (P<0.05,P<0.01), with the feeding rate decreasing by 43.89% compared to the control group. (2) With the increase of Cd²⁺ concentration, the accumulation of Cd in tissues was significantly higher in the experimental groups than that in the control group. (3) The total antioxidant capacity (T-AOC) and content of MDA in the water flea increased gradually with the concentration level of Cd²⁺. In the group with Cd²⁺ concentration of 0.09 mg/L, the levels of T-AOC and MDA increased significantly (P<0.05) compared to the control group. T-AOC was negatively correlated with the feeding rate whose correlation coefficientR² were 0.9521 and 0.9389, respectively. (4) The activity of AChE decreased with increasing Cd²⁺ concentration, especially when D. magna were exposed to higher concentrations of 0.05 and 0.09 mg/L (P<0.05). The results indicated that Cd²⁺ stress not only caused oxidative damage to water flea, but also induced the abnormal conduction function to the nerve system, which would result in inhibition of feeding behavior in D. magna.