Changes of surface shape, aggregate state, and microstructure of Apocynum fiber before and after irradiation were studied by XRD, IR, SEM, ESR, and solid state 13C CP/ MAS NMR. The results show that the surface shape and microstructure were not spoiled under 50 kGy gamma irradiation, while the crystallization of Apocynum fiber changed under 280 kGy. It also shows that different free radicals appear after irradiation and their concentration increases with the increase of irradiation dose.