Abstract: Dy_0.15Fe_1.85O₃ magnetic nanoparticles were prepared by coprecipitation method and lauric acid was performed to modify the surface of the magnetic nanopartiples. After claded by intermediate,the product were dispersed in silicon oil under the ultrasonic vibration,the magnetic fluids were obtained. The effect of lauric acid amount on saturation magnetization intensity and intermediate amount on magnetic liquid stability were studied. The properties of magnetic nanoparticles were characterized by transmission electron-microscopy （TEM）,X-ray diffraction （XRD）,the magnetic properties of magnetic nanoparticles and magnetic fluids were tested by super-conducting quantum magneto meter devices （SQUID） and Vibrating Sample Magnetometer （VSM）. The results show that the stability and magnetic properties of the magnetic fluid is best under the condition of lauric acid of 0. 05 g/g,the condition of intermedium of 0. 42~0. 58 g/g,the molar ratio of Fe²⁺ to Fe³⁺ to Dy³⁺ of 1: 2: 0. 011,the reaction of temperatures of 50℃.