Abstract: Co_x Fe_3-xO₄ ferrite films（x=0.2-0.8）have been synthesized on SiO₂ substrates by the sol -gel spin-coating technique.The magnetic properties,mierostructure and surface image of samples have been measured and analyzed by vibrating sample magnetometer,X-ray diffraction and atomic force microscope.Meanwhile,the magnetic properties and microstructure of Co_0.8Fe_2.2O₄ ferrite fihn have been situ measured at high temperature.The results at room temperature reveals that the peaks of spinel phase becomes higher gradually with increasing amount of Co²⁺ ions,and then single spinel phase exhibits when x=0.8,so better magnetic properties of samples have been obtained,the coereivity reaches 1.56×10~5 A/m,and the grain of samples is refined.The in situ measurement at high temperature shows that the coefficient of linear expansion of Co_0.8Fe_2.2O₄ film at 500℃is 1.3×10^-5 K^-1 ,the microstructures of cobalt ferrite films have good thermal stabilization.