ASP produced water has complex water quality, high salinity, high viscosity, high oil-containing emulsification, high content of small oil droplets, and difficult oil-water separation, which has an increasingly serious impact on oilfield production and the environment. Therefore, it has become an important task to carry out research on efficient treatment methods of ASP produced water. In order to improve the oil-water separation efficiency in ASP produced water, in this paper, using sodium carboxymethylcellulose (CMC) as the main chain, methacryloyloxyethyltrimethylammonium chloride (DMC) as the monomer, potassium persulfate (KPS) as the initiator, the cationic modified carboxymethyl cellulose graft copolymer (CDC) was prepared by aqueous solution polymerization, and applied to ASP produced water flocculation experiments. From the analysis of CDC feeding amount, flocculation temperature and CDC grafting rate, it is concluded that the flocculation effect of CDC is better than that of CMC. The optimal feeding amount of CDC was 50 mg/L, the flocculation effect did not change significantly when the flocculation temperature exceeded 45oC, and the optimal grafting rate of CDC was 77.5%.