Abstract: The ground simulation tests of proton irradiation for Kapton/Al films were conducted using the space synthesis irradiating facility, in which the energy of protons was chosen as 90 keV, and the flux was 5.0×1011 cm-2·s-1. The degradation of optical property was investigated through changes of the spectral reflectance of specimens before and after the irradiation. The damage mechanism was studied by means of ultraviolet/visible absorption spectra and Fourier transform infrared of spectra. The analysis results demonstrate that some complex reactions occurred in the surface layer of the specimens during the irradiation. The optical energy gap reduces gradually with increasing fluence. The red shift of the end absorption edge and a strong increase in absorbance in the visible region are evid