Etherified starch has the advantages of cheap raw materials and simple preparation process. In the field of wastewater treatment, it can be used as a flocculant and adsorbent. Amphoteric etherified starch CMGS was synthesized in a one-step method using cornstarch (St) as raw material, 2,3-epoxypropyl trimethyl ammonium chloride (GTA) and chloroacetic acid (CAA) as cationic and anionic etherification agents, respectively, and the flocculation performance on kaolin suspension was studied. The results showed that compared with cationic etherified starch, the optimal dose of the amphoteric etherified starch CMGS increased and the flocculation window length increased. The optimal dose of CMGS2 was 14 mg/L, and the flocculation window length was 24 mg/L, which has certain practical value.