A mixture of 3，3-bis（chloromethyl）oxetane （BCMO） and 3-ethyl-3-oxetane methanol （EHO） were used to synthesis the azide hyperbranched copolymers （r-POB-m） via cationic ring-opening polymerization and azidation reaction with different monomer molar ratio （BCMO/EHO=m）. The chemical structures were characterized with Infrared spectroscopy （FT-IR）， nuclear magnetic resonance （NMR）， gel permeation chromatography （GPC） and elemental analysis. The results showed that the copolymer has high molecular weight （>4400 g·mol^-1）， high nitrogen content （up to 43%） and controllable branching structure. X-ray diffractometer （XRD）， Hacker rheometer and differential scanning calorimeter （DSC） were utilized to characterize crystallinity， viscosity and chemical compatibility respectively. When m=4， r-POB-4 is amorphous， possesses the lowest process viscosity and has good compatibility with the main components of the propellant， indicating that it is a potential candidate for plasticizer. In addition， compared with the GAPA plasticizer， the energetic thermoplastic elastomer （ETPE）-based propellant with r-POB-4 plasticizer exhibits higher elongation at break， lower consistency coefficient and lower viscous flow activation energy， suggesting that the azide hyperbranched copolymer could be applied as the plasticizer to effectively improve the mechanical properties and processing properties of the propellant.