Changes of the free radical and chemical components and structures of the moso bamboo irradiated with UV-B are analyzed. Electron spin resonance (ESR) and X-ray photoelectron spectroscopy (XPS) are used to measure the spectrum of the free radicals and the X-ray photoelectron spectroscopy of the UV-B-irradiated bamboo powder. The testing results reveal that when the spectral splitting factor of the bamboo free radicals (g) is 2.003 3, the intensity of free radicals increases with the irradiation time according to the law: Y=1－e－biPt; after 60 mins of irradiation with UV-B, the O/C atomic ratio in the surface bamboo increases slightly; C-C and C-H contents increase; C-O and C=O contents decrease; -O-C=O contents increase to about 3 times than the original one, which indicate in the moso bamboo surface some oxygen-containing functional groups occurr and carbon oxidation state increased.