The initial decomposition of the condensed phase ANPyO crystal at various temperature (T=1500 K、2000 K、2500 K、3000 K and 3500 K) were studied by using ReaxFF reactive molecular dynamics simulation. The time evolution curve of the potential energy can be described reasonably well by a single exponential function from which the initial equilibration and induction time as well as the overall characteristic time of pyrolysis were obtained. Afterward, the activation energy E_a (88.65 kJmol^-1) also was obtained from these simulations. Result show when the ANPyO molecules in the unit cell almost decomposed, the potential energy of the system significantly attenuated. Meanwhile ANPyO showed different reaction mechanisms at different temperatures. At lower temperatures (1500 K≤T≤2500 K) the hydrogen from NH₂ transferred to ortho—NO₂ and promote C—NO₂ bond fission, while the H₂O and NO molecules formed. At very high temperatures 2500 K≤T≤3500 K), the C-NO₂ homolytic cleavage and C—NO₂→C—ONO rearrangement hemolysis are thermo dynamically favorable pathways in the early thermal decomposition of ANPyO. According to calculations using limited time steps, the main products are H₂O、N₂、NO₂、NO、CO₂、CO、OH and HONO. Secondary products are mainly NO₂、NO、OH and HONO, which has strong oxidizing property, so that the distribution has a dramatic fluctuation characteristics. It is found that H₂O and N₂ are the main stable products of thermal decomposition. Pyridine ring fission does not take place until most of the attached groups have interacted or disconnected, and increasing temperature accelerates fission of Pyridine ring and further decomposition to generate both CO₂, CO, NO, and amount of carbon-containing clusters.