To systematically understand the effect of ammonium perchlorate (AP) on the thermal decomposition mechanism of 5,5'-bitetrazole-1,1'-dioxadihydroxyammonium(HATO), the thermal decomposition characteristics, gas products and condensed phase change of HATO and HATO/AP blends were analyzed by combination of thermogravimetry-mass spectrometry-Fourier transform infrared spectroscopy (TG-MS-FTIR), differential scanning calorimetry(DSC) and Fourier transform infrared spectroscopy (FTIR). HATO had two consecutive thermal decomposition stages,while HATO/AP blends had three. For HATO/AP blends, the melting profile of AP disappeared; the thermal decomposition of HATO showed an advanced initial temperature, prolonged decomposition time and unchanged completeness of HATO decomposition. The gas products from the thermal decomposition of HATO were CO₂, N₂O, HCN, NH₃, NO, N₂ and H₂O; whereas CO₂, N₂O, HCN, NH₃, NO, N₂, H₂O, HCl and NOCl were detected for HATO/AP blends. The activation energy of HATO and HATO/AP blends tetrazole ring, which was calculated by equal conversion rate method was 53.38kJ·mol^-1 and 60.69 kJ·mol^-1,respectively. By comparing the thermal decomposition process of HATO and HATO/AP blends and the change of characteristic groups of condensed phase, the advancement of thermal decomposition temperature of HATO can be attributed to the proton transfer between the ammonium ion of AP and HATO. The prolonged decomposition time for HATO/AP blends might be explained by following mechanism: NH₃ was produced from the HATO and AP, which further reacted with the thermal decomposition intermediate 1,1'-dihydroxy-5,5'-tetrazolium (BTO) to form Diammonium 5,5'-bistetrazole-1,1'-diolate (ABTOX).