Temperature sensitive polymer (poly N-isopropylacrylamide, NIPAAm) was grafted successfully on the surface of cotton cellulose fabric by γ pre-irradiation-induced grafting. The effects of absorbed dose,dose rate,grafting temperature and concentration of monomer on grafting yields were investigated. In order to explain the characteristic of active points and their location in cellulose structure, the generation and decomposition of the peroxides formed during irradiation in air were measured. It was proved that the trapped radicals which made main contribution to grafting copolymerization reaction were mainly located in the third phase between the crystalline and amorphous regions of the samples and the grafted chains,at least part of them, were extended into the crystallinity. It was also found that besides the trapped radicals,the peroxides produced made some contribution to graft reaction even the graft temperature was lower than their decomposition temperature for NIPAAm with special structure. Reaction mechanism was discussed in details.