Abstract: The magnetic nanoparticels Fe3O4 were synthesized through hydrothermal reaction. Then, Core-shell structural Fe3O4@SiO2 particles with controllable size were prepared by hydrolysis and condensation of TEOS using Fe3O4 nanoparticles as seeds with the method of sol-gel. The prepared composite particles were characterized by HRTEM, FT-IR, XRD, VSM, respectively. In addition, the effects of volume ratio of alcohol to water, the concentrations of NH3·H2O and TEOS on the morphology of the nanocomposite particles were investigated. With the increase of TEOS concentration in the range of 0～0.05 mol/L, the thickness of the SiO2 shell increases on the condition of 0.3 mol/L of NH3·H2O and 4∶1 ratio of alcohol to water, and the morphology of the composite particles becomes more uniform.