The invention discloses a preparation method of a namometer PAFSI-graft modified starch hybrid flocculent. The preparation method is characterized by comprises the steps that 20 parts of Na2SiO3 and 350 parts of deionized water are added to a reaction bottle, the pH value ranges from 2 to 5, the room temperature reaction is performed for 2-3 h, and activated silicic acid is prepared; a certain amount of AlCl3 and FeCl3 ethylene glycol solution is added slowly in 20 parts of activated silicic acid for reaction, 1-5 parts of CTAC (cetanecyl trimethyl ammonium chloride) is added after cooling, curing is performed, and namometer PAFSI is prepared; 20 parts of starch and 20-400 parts of deionized water are added to the reaction bottle, N2 is fed, the starch is cooled to 30 DEG C after gelatinized for 0.5-1 h under stirring and at the temperature of 65 DEG C to 90 DEG C, 0.5-6.0 parts of CTAC is added, 2-10 parts of nanometer PAFSI is added, the pH value ranges from 5 to 7, 0.05-0.5 part of potassium persulfate and 0.02-0.3 part of sodium sulphite are added at the temperature of 30 DEG C to 55 DEG C, 3-10 parts of cationic monomers and 2-10 parts of macromonomers are added slowly, N2 is fed, the reaction is performed for 4-8 h, and the namometer PAFSI-graft modified starch hybrid flocculent is prepared.