Using butanediol as initiator, boron-trifluoride etherate as catalyst， 3-azidomethyl-3-methyloxetane homopolymer (PAMMO) was synthesized by the cationic polymerization of 3-azidomethyl-3-methyloxetane(AMMO) which was carried out in dichlorometane. The effect of catalyst concentration on polymerization was studied by experiment.The structure and properties of PAMMO were also characterized by DSC, TGA and IR measurements. The results show that the polymerization can be controlled by decreasing catalyst′s concentration .The glass transition temperature（T_g） of PAMMO was 40.3 ℃. PAMMO can be used as the liquid energetic binder of cast propellant and the soft segment of energetic thermoplastic elastomer.