The rapid pyrolysis of GAP/AP system under simulated combustion conditions was investigated by an on-line analysis, i.e. so called T-Jump/FTIR. The results show that the compositions of the main gaseous products for pyrolysis are changed, in comparison with the pyrolyses of single, which indicates that the interactions occur between the components of GAP/AP system. From an obvious effect of pressure on the main gaseous products for GAP/AP pyrolysis it is shown that the interactions between GAP and AP components arise from the gaseous products of AP and both the reactions in gas phase and in gas/condensed phase occur in the GAP/AP mixed system. The interactions between GAP and AP are not affected by test temperature. It is considered that the real time analysis of gaseous products of energetic material pyrolysis under simulated combustion conditions would be carried out by T-Jump/FTIR on-line analysis technique and from microcosmic reaction a technical approach used to explore the rapid pyrolysis of energetic materials and interactions between their components at high temperature and pressure would be developed by the on-line analysis technique from microcosmic reaction.