To explore the effects of hydrodynamics on plankton, four kinds of surface flow enclosure experiments were done from August, 2007 to July, 2008. The flow velocity were 0.002, 0.10, 0.15 and 0.30 m x s(-1) respectively. Under 0.15 and 0.30 m x s(-1) surface velocity conditions, it was revealed that Spirogyra biomasses were 2.3 times and 31.3 times of the ones under static state respectively. Under 0.10, 0.15 and 0.30 m x s(-1) conditions, Chl-a concentrations were 45%, 54% and 26% of the ones under statistic state while zooplankton biomasses were 38%, 27% and 6% respectively. The mechanism is that a certain flow velocity stimulates Spirogyra growth may be for the shear stress generated by the surface flow can help the vegetative reproduction. Shear stress and turbulence may also bring the phytoplankton to the light limited area by force. Besides, as Spirogyra grows well, it can inhibit the phytoplankton growth by excretion or some symbiotic microorganism. When shear stress or water turbulence exceeds a certain value, crustacean zooplankton successful grazing rate may also be depressed.