[Purposes] In order to improve the chemical coagulation method for treating cyanobacterial blooms and solve the problems of algal flocs separation and collection, chemical conditions of coagulation were optimized to increase removal efficiencies of target pollutants and reduce the risk of secondary pollution. [Methods] Based on the water quality characteristics of algae-laden water in Changsha section of Liuyang River, a new method of coagulation treatment with self-floation was proposed. Aluminium salts, ferrous salts, hydrophilic silicon dioxide and sodium carbonate were used to treat algae-laden water. The optimal coagulation parameters for algae and phosphorus removal were determined by the quadratic regression model of the response surface methodology. The coagulation mechanism and self-flotation characteristics were discussed by combining coagulation effect and characterization analysis of algal flocs. [Findings] When n(CO[23]-)∶n(Fe+Al) （n for the amount of matter）and m(Si)∶m(Fe+Al) （m for mass）were of 1.75∶1 and 1∶2 respectively, and the coagulant dosage was of 0.525 mmol/L, the highest removal efficiency of algal cells and total phosphorus, as well as the best degree of algae flocs self-flotating were achieved. Residual aluminum and iron concentrations were within the limit values of water quality standard. The self-floating coagulation treatment of algae-laden water was decided by the complex interactions between target pollutants and hydrolysis products of aluminum salt, ferrous salt, and hydrophilic silicon dioxide. In the early stage of coagulation, algal cells were destabilized and coagulated by compression of double electronic layer and electronic neutralization. In the middle and late stages of coagulation, target pollutants were removed by adsorption bridging, sweeping flocculation and functional groups of Si―C. The removal of total phosphorus and residual aluminum/iron depended on the formation of Fe3(PO₄)2·H2O and AlPO₄. Effective control of residual aluminum/iron was related to the adsorption of hydrophilic SiO₂. The algal flocs could be adhered with CO₂ bubbles generated by double hydrolysis reaction between Fe2+ and CO[23]- through collision to achieve self-flotation. [Conclusions] The treatment of algae-laden water by self-flotation coagulation method is highly efficient, stable and safe, with great application potential in emergency treatment or long-term treatment of algae pollution in the Dongting Lake water system.