The thermal decomposition of AlH₃, glycidyl azide polymer(GAP) and AlH₃/ GAP mixed system were studied by in-situ thermolysis-fourier transform infrared spectroscopy(FTIR) coupling techniques. Results show that AlH₃ begins to decompose when temperature raises to 100 ℃ and the decomposition rate reaches the maximum at 180 ℃. The azide group of GAP begins to cleavage to imine intermediate at about 200 ℃. The main chain of GAP completely depolymerization is lagging behind. The decomposition process of GAP is changed by AlH₃. AlH₃/GAP system loses mass when temperature raise to 170 ℃, and during the decomposition of AlH₃/GAP, Such unsaturated bonds as C＝N and C＝O are not observed. The possible reason is the strong reduction of AlH₃.