[Objective] To study the flocculation effect of bacterial strain xn-1 on water bloom causing species-Microcystis aeruginosa, to control water bloom. [Methods] Flocculation bacterium was isolated from phycosphere based on plate spread and streak technique; 16S rRNA gene was applied to determine the evolutionary status. Flocculation mechanism was confirmed by addition of different metal ions as coagulants. Bioflocculant was obtained by gradient alcohol precipitation. Microplate reader was used to study flocculation activity. [Results] Strain xn-1 was determined as a species of the genus Shinella, designated as Shinella sp. xn-1. Strain xn-1 exhibited high flocculation activity on M. aeruginosa with adding Ca2+ as coagulants, and the flocculation activity was originated from extracellular supernatant, showing high flocculation efficiency with the concentration of 3.0%. Bioflocculant isolated from extracellular supernatant could exhibit high flocculation effect with the addition of 0.5 g/L, and the algal flocs became huger with the increase of processing time. [Conclusion] Shinella sp. xn-1 shows high flocculation activity on M. aeruginosa through secreting extracellular bioflocculant, and the flocs with large volume are formed under the flocculation effect. This study is a useful option to control water blooms in the future.