According to the algae outbreak (the dominant species was synedra acus belonging to Diatoms) in source water, the effects of PAFS, PAC, and PFC coagulants on algae removal and turbidity removal were compared. PAFS was chosen as the optimal coagulant. In addition, different pro-oxidations and coagulant aids were added to enhance flocculation removal effects of algae. The experimental results show that PDMDAAC combined with PAFC shows the best effect, and the order of other promoting coagulation effect was PPC>ClO2>PAM>H2O2>HCA-1. Based on the box-Behnken Design(BBD) experiment design principle, the effects of pH, stirring rate and stirring time on algae removal using PAFS+PDMDAAC were investigated. The results show that the three factors play significant effect on the removal of synedra acus, and the influence degree is pH>stirring rate>stirring time, while the interactive influence of the three factors is not significant. Moreover, the optimum condition of enhanced coagulation is obtained, in which pH is of 7.5, stirring rate is 75r/min and stirring time is 15 min, and the alga removal effect is 98.75%.