Abstract: Spinel CoFe2O4 nanoparticles were synthesized by hydro-thermal method. The effects of synthetic temperature and Co contents in raw materials on the structure, morphology and magnetic properties of synthetic particles were studied by X-ray diffractometer, field emission scanning electron microscopy, transmission electron microscopy and vibration magnetometer, changing synthetic temperature (140-220 ℃) and Co contents in raw materials, and the effects were explained in mechanism. The results show that the average grain size of CoFe2O4 nanoparticles synthesized by hydro-thermal method was between 30 nm and 40 nm. It was advantageous to raise Co contents in raw materials for removing α-Fe2O3 phase. The saturation magnetization of particles raised continually with the increase of the synthetic temperature and its maximum was 59.694 Am2·kg-1, the coercive force raised first and dropped later and its maximum was 1 273.28 A·m-1.