Harvesting is one of the most critical processes in large scale microalgae culture， which occupies 20%~30% of total costs. As a flocculant, flocculation effect and kinetics of PAC were investigated on harvesting Chlorella sp., and the economic evaluation for harvesting microalgae was conducted. Different dosages of PAC were added into microalgae suspension, after stirring at 200r/min for 1min, the content of Chlorophyll was measured at different time. The results showed that five different dosages of PAC exhibited a high flocculation efficiency over 86% after 8min. The flocculation efficiency increased significantly (P<0.05) with increasing PAC dosage. The flocculation efficiency reached to 986% when the dosage of PAC was 123 5mg/L, and the residual aluminum concentration was 1328mg/kg in Chlorella sp. biomass. The flocculation mechanism of PAC was charge neutralization and sweeping flocculation, which acted in combination. And the cost was RMB￥266.04 when flocculating microalgae biomass was 1kg, which was 68.8% lower than the cost of RMB￥853.39 by centrifugation. The results of indicated that the flocculation of PAC obeyed the second order kinetics. Flocculation with PAC is feasible for harvesting microalgae.