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This study explored the feasibility of calcium peroxide (CaO 2) to inhibit cyanobacterial blooms of the outbreak and dormancy stages. Our previous studies have found that CaO 2 has a high inhibitory effect on cyanobacteria. In order to explore the application effect of CaO 2 in actual cyanobacteria lake water, we conducted this study to clarify the effect of CaO 2 on inhibiting cyanobacteria in outbreak and dormancy stages. The results showed that CaO 2 inhibited the growth of cyanobacteria in the outbreak and dormancy stages by 98.7% and 97.6%, respectively. The main inhibitory mechanism is: (1) destroy the cell structure and make the cells undergo programmed cell death by stimulating the oxidation balance of cyanobacteria cells; (2) EPS released by cyanobacteria resist stimulation and combine calcium to form colonies, and accelerate cell settlement. In addition to causing direct damage to cyanobacteria, CaO 2 can also improve water quality and sediment microbial diversity, and reduce the release of sediment to phosphorus, so as to further contribute to cyanobacterial inhibition. Finally, the results of qRT-PCR analysis confirmed the promoting effect of CaO 2 on the downregulation of photosynthesis-related genes (rbcL and psaB), microcystn (mcyA and mcyD) and peroxiredoxin (prx), and verified the mechanism of CaO 2 inhibition of cyanobacteria. In conclusion, this study provides new findings for the future suppression of cyanobacterial bloom, by combining water quality, cyanobacterial inhibition mechanisms, and sediment microbial diversity. [Display omitted] • CaO 2 inhibited the growth of cyanobacteria during outbreak and dormancy stages. • CaO 2 inhibited cyanobacteria through oxidative stimulation and colony formation. • 100 mg L−1 CaO 2 enhanced microbial diversity. • Providing the practical application effect of treating cyanobacteria with CaO 2. [ABSTRACT FROM AUTHOR]