The microstructure and thermal property of 25 μm graphite film under the condition of vacuum proton irradiation with an energy of 100 keV and a maximum fluence of 2.5×10¹⁵ p/cm² were studied. The microstructure was analyzed by Raman， XRD and XPS methods， thermal performance was analyzed by using laser flash analysis （LFA）. The interplanar spacing of the graphite film is 0.335 83 nm， and the degree of graphitization is 95.0%. The results show that proton irradiation can lead to defects in the surface layer of the graphite film， the interlayer spacing increases， the degree of graphitization decreases， and the oxygen content increases； the integral area ratio of the D and G peaks in the Raman spectrum indicates an increasing defect density as the proton irradiation dose increases. The thermal diffusivity of 25 μm graphite film has no obvious change after proton irradiation with energy of 100 keV and injection fluence of 2.5×10¹⁵ p/cm².