3,3-bis(bromomethyl)oxetane-r-glycidyl azide copolymer was synthesized by cationic copolymerization,using butane-1,4-diol and boron trifluoride etherate as the initiator and catalyst,followed by the azidition of the halogenated copolymer.n(BF3-dimethyl ether complex)/n(1,4-butylene glycol)(n(BTFE)/n(BDO))=1∶2,15 ℃ was chosen as better experimental condition for the cationic copolymerization.FT-IR,13C-NMR,GPC and DSC were used to characterize the copolymer.The results show that n of the copolymer is 1750 and the molecular weight distribution is 1.12.The content of the oligomers is about 22 percents by weight.DSC shows that Tg of the product is-57.68 ℃,and the crystallization of 3,3-bis(azidomethyl)oxetane(PBAMO) was disturbed by the addition of glycidyl azide polymer(GAP).