To explore the indicating functions of bacterioplankton community to water environments in a regulated fragmented river, the spatiotemporal investigations were carried out along the five cascade dams in the main channel of the North River (China) during 2019. Our results indicated that bacterioplankton community was good bioindicators of temporal variations, which was well exhibited by the class level, since the most dominant bacteria class (Gammaproteobacteria, Oxyphotobacteria, Actinobacteria) and sub-dominant bacteria class (Bacteroidia, Betaproteobacteria, Acidimicrobiia) showed obvious temporal variations. And rainfall, WT, SD and pH were responsible for temporal variations. The indicating functions of bacterioplankton to spatial variations were only exhibited by individual dominant bacteria class in individual period, and rainfall, TP and pH were responsible for spatial variations. The clustering results based on similarities of bacterioplankton community showed that temporal differences absolutely suppressed the spatial differences, which was in accordance with environmental parameters that most parameters exhibited obvious temporal differences but few exhibited spatial differences. The possible reason might be that the river fragmentation caused by cascade dams weakened the spatial differences, and WT, rainfall and river runoff played key roles for this pattern. In conclusion, the bacterioplankton community could be good bioindicators to water environments in this fragmented river ecosystem, and its indicating functions played more important role in temporal variations.