In this study, a new inorganic–organic composite flocculant CSSAD was prepared by the reaction of corn starch (st), acrylamide (AM), and (2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) with a previously prepared SiO 2 sol by using the aqueous solution polymerization process. The different factors affecting the preparation were investigated and the optimal synthesis conditions were established: polymerization temperature was 70°C, reaction time was 4h, w(DMC):w(st) was 1.5, w(AM):w(st) was 3, and the ratio of initiator to acrylamide was 0.5wt.%. CSSAD was characterized by FTIR spectroscopy, scanning electron microscopy, and gel permeation chromatography. The different factors affecting the flocculating ability of CSSAD for waste drilling fluid were studied. These factors included the dose, stirring rate, and time. When the dosage of CSSAD was 0.3g (per 100g waste drilling fluid) with a stirring rate of 60r/min and a stirring time of 2min, the water content of the flocculated precipitate was the lowest at 21.34%. And CSSAD showed better flocculating ability than other flocculants in the same dose (0.3wt.%).