Abstract: For enhancing the coal slurry treatment efficiency in coal washery,acryl amide is grafted onto the large molecules of corn starch using ammonium cerous sulfate as initiator. And then,orthogonal experiment is conducted for determining the optimum graft modifications conditions and the degree of the effect on slurry sedimentation produced by the modified corn starch. Result of investigation indicates that when the starch and the initiator are added at rates of 10. 50 g and 0. 02 g respectively,and the grafting duration is 2. 50 h under a temperature of 65 ℃,a best grafting result can be expected. After the addition of modified corn starch,the turbidity of the water after precipitation is reduced down to 10% of its original value in a time period of only 50. 80 minutes.