In this paper, Fe₃O₄ nano-particles modified by oleic acid were synthesized through coprecipitation method. The Fe₃O₄ nano-particles were dispersed into Octane to form magnetofluid. Then, Fe₃O₄@PS microspheres were prepared using one step miniemulsion polymerization method. SEM results showed that the particle size of Fe₃O₄ nano-particles is about 13 nm and the diameter ofFe₃O₄@PS microspheres is 120~150 nm or so. The magnetic measurement results showed that as-prepared Fe₃O₄@PS microspheres possess superparamagnetism and the saturation magnetization Ms is about 25 emu/g. The surface of Fe₃O₄@PS microspheres is negatively charged and the Zeta potentialis －60 mV. Reflectance spectrum measurement results showed that the colloidal suspension of Fe₃O₄@PS in aqueous solution exhibits bright structural color and obvious band-gap features under magnetic fields. With the increase of magnetic field strength, reflectance peaks wavelength can be modulated in the range 450 ~ 650 nm.