Abstract: In view of the problems in Daqing oilfield such as the waste water composition is complicated, the flocculant and coagulant dosage is large, and the cost is high, etc, by taking the sewage in Longyi Union Station of No.9 Plant as the research object, the study on the selection of coagulant and flocculant, coagulant and flocculant flocculation effect under different dosing concentration, etc. were carried out. From five kinds of coagulants and six kinds of flocculants, better potions were selected, and then the optimum coagulant and flocculant distribution system were determined. The experimental results show that the optimal mixing system is the coagulant GYT and flocculant MT, the turbidity removal rate and oil removal rate are 97.42%and 91.27% respectively, and the suspended solid content is 12 mg/L, which provides the corresponding theoretical and experimental basis for ensuring that the return water injection of the oilfield meets the field requirements of Daqing oilfield.