Abstract: Fe₃O₄ magnetic nanoparticles were first prepared using the coprecipitation method and were coated by SiO₂. Functional magnetic nanometer materials were then obtained through bonding polyethylenimine(PEI) on the surface of SiO₂ and quaternarization with benzyl chloride. Coating of SiO₂ could increase the dispersion and stability of Fe₃O₄ nanometer materials. FT-IR,SEM,TG and vibrating sample magnetometer were used to characterize the magnetic nanomaterials. The results showed that the synthesis of magnetic nanomaterials was successful. The static adsorption method was employed to study the adsorption properties of magnetic nanomaterials towards Cr₂O₇^2- and various factors which might influence the adsorption performance of the materials. The optimal conditions for the separation and enrichment environment of heavy chrome acid radical are:acid medium,the temperature is 25℃,potassium dichromate concentration is 0.8 g/L,the adsorption quantity for 120 mg/g,grafting,the greater the amount of adsorption quantity increase.