Abstract: During the large-scale production of microalgae, harvesting technology is one of the important steps,and is one of the key factors currently restricting the algal industrialized development. In this study, alum was used as a flocculant to investigate the effects of alum concentrations, initial OD values, and flocculation time on the flocculation efficiency of Chlorella sorokiniana. And on this basis, response surface methodology was applied to optimize the flocculation process of C. sorokiniana using alum. It was hoped that these results would provide technical support and data reference for large-scale harvest of this alga. Main experimental results were as follows:（1）alum concentrations, initial OD values, and flocculation time had significant effects on the flocculation efficiency of C. sorokiniana（P＜0.05）, the factors that affected the flocculation efficiency were in the order of alum concentrations ＞ initial OD values ＞ flocculation time;（2） the highest flocculation efficiency of C. sorokiniana（98.48%） was obtained under the optimal technological conditions for flocculation process of this alga, which were 1.2 g/L of alum, 0.8 of initial OD value, and 30 min of flocculation time.