A cyanobacterial (Arthrospira platensis) bloom was induced in situ by nutrient manipulation in an enclosure. The succession of the phytoplankton community and the water chemistry variations before the appearance of bloom, as well as their relationship, were investigated. The cell pigment variations were studied simultaneously. The Pearson’s correlation analysis showed that there was no significant correlation between water chemistry and green algal or cyanobacterial composition, indicating that water chemistry variations were not suitable to be used as indicators for cyanobacterial-bloom early-wing. However, the diversity index of the phytoplankton community decreased sharply before the bloom appeared. Therefore, the dynamics of phytoplankton community was put forward to be an indicator for cyanobacterial-bloom early-wing. In addition, the cell pigment variations represented the changes of community structure, which should be useful for studying the dynamics of phytoplankton community.