The multifunction w ater treatment reagent FIQ -C has been synthesized through chemical modification with the natural polymer F₆₉₁ powder.Factors af fecting the preperation are studied and the best reaction conditions are found by the optimizat ion experiment s.Experimental result s show :the relative viscosi ty is up to 3.1 (0.5 %)and the density of cationic quaternary ammonium g roup is up to 55 %w hen the reaction temperature is 50 ℃, the reaction time is two hours, NaOH (to F691)is 0.4 g/g and the feeding ratio of the raw material is 1.6.The structures of polymers are characterized by FTIR method.FIQ -C had good efficiency of f locculation, corrosion inhibition and scal inhibition.