A kind of silica-coated magnetic nanomaterials modified with 1-octyl-3-methylimidazolium hexafluorophosphate（［OMIM］PF6） was prepared,and characterized by scanning electron microscope（SEM）,Fourier transform infrared spectroscopy（FT-IR）,vibrating sample magnetometer（VSM） and thermogravimetric analyzer（TGA）.The synthetic material（Fe3O4-SiO2-IL） showed a good acid resistance.The adsorption behavior of cadmium ion onto Fe3O4-SiO2-IL was tested,and it was found that the equilibrium adsorption followed Langmuir isotherms well.Based on this,a new method for separation and preconcentration of Cd2+ in aqueous solution was developed by using modified silica-coated magnetic nanoparticle as the sorbent and flame atomic absorption spectrometry（FAAS） as detector.Ｅffects of some factors on recovery of Cd2+ were investigated.The optimum conditions were　as the follows：pH 6.0;eluent：1 mol/L HCl;oscillation time：10 min;standing time：20 min.Under the optimized conditions,the limit of detection（LOD） for Cd2+ was 0.2 μg/L,and relative standard deviation（RSD,n=6） for 15 μg/L Cd2+ was 2.5%.The proposed method was applied in the determination of Cd2+ in river and lake water with spiked recoveries of 84%-100%.