To analyze and compare the thermal stability of commercial ammonium nitrate (AN) and homemade non-explosive and irrestorable fertilizer-grade ammonium nitrate (NEIFAN), the crystal transformation changes, thermal decomposition characteristics and adiabatic decomposition processes of AN and NEIFAN were studied by thermogravimetry (TG)-differential thermal analysic (DTA)-derivative thermogravimetry (DTG), differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC). The curves of thermal decomposition temperature and pressure vs time, self-heating rate and pressure vs temperature for AN and NEIFAN under the adiabatic decompositions condition were obtained. The kinetic parameters (apparent activation energy and pre-exponential factor) of pseudo zero order adiabatic decomposition reaction for AN and NEIFAN were calculated. The results show that in comparison with AN, the crystal transformation peak at about 88 ℃ of NEIFAN disappears, revealing that NEIFAN has better thermal physical stability. The decomposition peak temperature of NEIFAN obtained by TA-DTA-DTG and DSC curves and the apparent activation energy of the pseudo zero order adiabatic decomposition reaction of NEIFAN obtained by ARC data are much higher than those of AN, indicating that NEIFAN has a higher heat-resistance ability than AN. Considering that the increase of physicochemical stability of NEIFAN is attributed to the joint action of inorganic and organic additives in NEIFAN.