In order to meet the requirements of explosives， thermoplastic elastomers with different number-average molecular weight （M_n） were prepared. Controllable polymerization and application of glycidyl azide polymer （GAP）-based energetic thermoplastic elastomers （GETPE） were conducted. The influence of polymerization medium and solid content on controllable polymerization of GETPE was investigated， and on-line viscosity monitoring on M_n was explored. The results show that M_n of GETPE can be accurately controlled by on-line viscosity monitoring. The error of M_n in the range of 20000-50000 can be tuned within ±2000， and the error rate can be controlled within 5%. GETPE has excellent compatibility with commonly used explosives and good application potential in high solid content propellant and high energy polymer bonded explosives （PBXs）.