Energetic thermoplastic polyurethane elastomers (ETPUs) of glycidyl azide polymer (GAP) were synthesized on GAP/poly(caprolactone)(PCL) (100/0, 50/50) as a soft segment and methylenebis(phenylisocyanate) (MDI) extended 1,5-pentanediol as a hard segment by solution polymerization in dimethyl formamide (DMF). Differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) were used to examine the thermal decomposition behavior. Kinetic analysis was performed with model fitting and a model-free method to obtain the activation energy as a function of the extent of conversion. ETPU decomposition was divided into two stages with different activation energies. The first main weight loss step corresponds to the elimination of $N_2$ from the decomposition of $-N_3$ bonds within azide polymers. The activation energy of the main decomposition of GAP ETPU and GAP/PCL ETPU was approximately 190 kJ/mol. The second weight loss step coincides with the decomposition of the skeleton. The activation energy of those showed an increasing trend.