Abstract: CR39 samples were irradiated with sulphur ions from HI-13 tandem accelerator to produce latent tracks at China Institute of Atomic Energy. Ultraviolet light with wavelength 360 nm was used to sensitize the bombarded CR-39 samples before chemical etching by NaOH solution. The latent tracks were then developed into pores or holes with certain diameter. Silver black was coated on the surface of etched CR-39 using evaporation in inert gas argon ambience. The SEM images indicate that the silver nano-particles are 60-100 nm in diameter at the pressure of 50-100 Pa, and the diameter of spherical clusters formed by nano-particles is 3 μm. The reflectivity indices were measured for all CR-39 samples, untreated and treated with above-mentioned procedures, within the wavelength of 2.5-25 μm. The results indicate that CR-39 modified with a combination of solid state nuclear tracks and silver black coating can decrease the reflectivity index to 0.9% for the wavelength range of 8.0-25 μm, and that is 82% reduction compared to CR-39 without modification. The blank reflectivity indices of CR-39 at wavelength of 5.8 μm and 7.8 μm are reduced from 9.0% and 13.0% to 5.0% and 6.8%, respectively.