Abstract: The ultraviolet (UV) photodecomposition of solid HNS (2, 2, 4, 4, 6, 6-hexanitrostillbene) under irradiation of UV light has been studied by different experimental means, including UV-Vis spectra, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectra (EPR) and mass spectra (MS). Two new peaks locating around 310 nm and 350 nm appear in the UV-Vis spectra of HNS/acetonitrile solution after UV light irradiation. Similarly, after laser irradiation, two new peaks appear at the binding energy of 401 eV and 528 eV for N 1s and O 1s XPS narrow scan spectra, respectively. Furthermore, the mass spectrum shows two new characteristic ion peaks corresponding to mass-charge ratio of 403 and 329. Experimental results indicate that CNO2 broken and nitro-nitrite isomerization with subsequent release of NO are the main photolysis pathways during the photodecomposition of HNS.