The coagulation effect and floc characteristics of M. aeruginosa, Synedra and Anabaena were studied, separately, by using ferric chloride and aluminum sulfate coagulants. The results show that the ferric salt has better coagulation and removal effect on the three algae species than aluminum salt does, and the three algae species achieves best coagulation effect when the ratio of coagulant is ferric salt coagulant > aluminum salt coagulant. The M. aeruginosa has the worst coagulation effect, and Synedra has the best under different dosages of ferric and aluminum salts. Compared with the use of aluminum salt, the three algae flocs coagulated by iron salt have larger fractal dimension. The fractal dimension value of Synedra is the largest(the maximum value:1.72) and that of M. aeruginosa is the smallest(the maximum value:1.17), indicating the effect of algae morphology on the flocs structure. The particle size(d₅₀) of the flocs of the three algae species when coagulated with ferric salt is larger than that of the flocs using aluminum salt, and the strength and recovery factor of the ferric salt flocs are smaller than those of the aluminum salt flocs. The maximum value of d₅₀ of M. aeruginosa floc (632 μm) is smaller than that of Synedra floc (765 μm) and Anabaena floc (777 μm) when using ferric salt. Synedra has the largest recovery factor of 26.54%, and Anabaena has the smallest recovery factor of 11.04% when using ferric salt. When the three algal flocs reach the isoelectric point, the dosage of ferric salt is greater than that of aluminum salt. The zeta potential of algal floc can be used to analyze the dosage corresponding to the optimal removal rate of algae coagulation. The M. aeruginosa flocculation is mainly electroneutralized, while the adsorption bridge and netting may play a more important role in the flocculation of Anabaena and Synedra.