In September 2008, a meteorology-hydrology-water quality simultaneous observation was conducted to study the influences of prior wind field on hydrodynamic characteristics and cyanobacterial bloom in northern bays(Meiliang Bay and Gonghu Bay) of Lake Taihu. The results showed that exposed to prior wind field, the surface, middle and bottom water layers flowed out of the bays. There was no compensation current in the two bays. Surface current field was sensitive to real wind field, but middle and bottom current fields lagged behind the wind changing. Influenced by southeast wind, a clockwise circulating current could be rapidly formed in the surface water layer of Meiliang Bay. In Gonghu Bay, the flow direction of surface current field did not change under the action of Westerlies, but its magnitude decreased obviously so that the current velocity increased with the water depth. The observation proves that hydrodynamic is very important for the stratification of chlorophyll-a concentration and drift of cyanobacterial bloom in northern bays of Lake Taihu. Cyanobacteria tended to accumulate and form bloom on water surface in low-hydrodynamic area. Under the condition of high-intensity disturbance, cyanobacteria mixed along the water depth. This can greatly decreased the risk of cyanobacterial bloom. Comparing with the influence of hydrodynamic, that of nutrients on the distribution of chlorophyll-a concentration was less important.