Abstract: Hydrophobically associated cationic starch(HACS) was synthesized by inverse suspension polymerization, in which the continuous phase was cyclohexane, dispersant was Span 80-Tween 80 and initiator was redox initiator. Effects of dispersant, reaction temperature and time on soluble properties and the grafting properties were discussed. The grafted product was characterized with IR and X-ray diffraction. The experiment results showed that copolymerization can be proceeded rapidly at low temperature, and the optimum reaction condition was as follows:ratio of m(St):m(AM):m(DMDACC):m(OA) 4:7.4:1.5:0.6, content of initiator 3.1 mmol/L, grafting temperature 30℃, reaction time 3 h. The monomer conversions is 92.6%, grafting rate is 53.8% and viscosity-average relative molecular weight (MV) is 3.26×106.