Algal blooms have occurred frequently in the backwater region of the Daning River branch since the impoundment of the Three Gorges Reservoir(TGR). In order to assess the water quality status and the driving factors on algal bloom outbreak, the water quality has been monitored since 2005, and 2 typical algal blooms, occurred in Dongpingba in March and May 2010, were investigated. Results showed that Daning River was mesotrophic and water quality was good, nevertheless the trophic grade was underestimated for the period of algal bloom outbreak. For algal bloom in March, there was a significant negative correlation between Chl. a concentration and velocity, while obvious relationships in Chl. a and pH or DO, indicating that velocity was an important factor for this bloom outbreak and pH, DO were sensitive factors caused by bloom. For algal bloom in May, there was a significant negative correlation between Chl. a concentration and velocity, while a significant positive correlation between Chl. a and flow quantity, and also obvious relationship in Chl. a and pH, SD. It indicated that velocity and flow quantity were important factors for algal bloom outbreak in May, and pH, SD became the sensitive indices. According to the operational schedules of TGR, March and May belong to the period with high water level and discharge, respectively. Schedule times with different hydrodynamics may be responsible for the difference of effect factors on algal bloom, but the mechanism need to be further studied. Results suggested that the algal bloom mechanism in the different operational schedules of TGR is different from each other significantly. Therefore, the study on algal bloom in backwater region of Daning River need to be performed according to the operational schedule of TGR.