To explore the effects of the H₂O and Fe(NO₃)₃ on the thermal stablility of NH₄NO₃, thermal analysis for different concentrations of NH₄NO₃(100%, 95%, 90%) solution and 95% NH₄NO₃ solution with different content of Fe(NO₃)₃ (1%, 2%, 3%, 4%)were studied by C80 micro thermal instrument in closed environment. Results show that the NH₄NO₃ solution activation energy rises with the decrease of the concentration of NH₄NO₃, and the difficulty degree of the thermal decomposition decrease. H₂O depresses the decomposition of NH₄NO₃, and increase its self-reaction. The onset temperature(T_onset) of 95%NH₄NO₃ solution is 238.89℃, and with the increase of ferric nitrate, its T_onset decreases. Fe(NO₃)₃ has a catalysis effects on the thermal decomposition of 95% NH₄NO₃ solution. T_onset of 95% NH₄NO₃ with 2% Fe(NO₃)₃ solution is 201.13 ℃.