用共沉淀法制备了CoFe2 O4 超细微粒 ,不用表面活性剂而通过控制酸蚀 ,合成了稳定的磁性液体 .通过X 射线衍射、振动样品磁强计、透射电子显微镜以及扫描隧道显微镜对微粒进行了分析 .对共沉淀 酸蚀法制备磁性液体的机理进行了探讨 . CoFe 2 O 4 ultrafine particles were prepared by co-precipitation method, and stable magnetic liquids were synthesized by controlling the acid etching without using surfactants. The particles were characterized by X-ray diffraction, vibrating sample magnetometer, transmission electron microscope and scanning tunneling microscope The mechanism of coprecipitation acid etching for preparing magnetic fluid was discussed.