Abstract: An iron oxide nanoparticles preparation system,which contained ultrasonic atomization,segmentally thermal decomposition and oxidation of iron pentacarbonyl,product collecting and modification,was established.The effect of different operating temperatures on phase composition and morphologies of the prepared nanoparticles were studied,and firstly used the method of adding modifiers in atomization liquid to control the sizes and dispersity of magnetic iron oxide nanoparticles products.The properties of nanoparticles were tested by X-ray diffraction（XRD）,transmission electron microscopy（TEM） and superconducting quantum interference device（SQUID） measurements.Spherical maghemite nanoparticles with different degree of dispersity and crystallinity were successfully synthesised,and SQUID test shows that with the decrease of size,the magnetism of maghemite nanoparticles changes from paramagnetic to superparamagnetic.