Abstract: Chaetoceros curvisetus is an important bloom-forming species in China. In this study, the growth characteristics of C. curvisetus at different growth phases and the changes of polyphosphate (PolyP) in algal cells at different phosphate concentrations were analyzed. It was found that under the condition of high phosphorus culture, the maximum cell density of C. curvisetus was 4.99×10⁹ cell/L, and the nuclear PolyP and short-chain PolyP in the initial phase were significantly higher than those in the growth phase, and the nuclear long-chain PolyP in the initial phase was significantly higher than those in the growth phase and maintenance phase (P<0.05). Under the condition of low phosphorus culture, the maximum cell density of C. curvisetus was 9.35×10⁷ cell/L, the long-chain PolyP in the cytoplasm of C. curvisetus in the growth phase was significantly higher than that in the maintenance phase. Whether under high or low phosphorus cultivation conditions, the total PolyP in the cells of C. curvisetus was negatively correlated with the cell density (P<0.05). In addition, the cell density of C. curvisetus was negatively correlated with the long-chain and short-chain PolyP in the nucleus under high phosphorus culture conditions, while it was negatively correlated with the long-chain PolyP in the cytoplasm and nucleus under low phosphorus culture conditions. The results of this study can provide a new theoretical basis for clarifying the storage and utilization mechanism of phosphate during the bloom of C. curvisetus.