Abstract: Relative pyrolyzate abundance(F )vs. the observed pyrolysis temperature(T p)curves of TTZ, HMX,RDX and DNT are obtained by means of Py/GC, particularly with the increase in pulse/step of the pyrolysis temperature. Physicochemical mechanism of materials in the special pyrolysis processes is discussed,and the model of thermal process of a material on the coexistence of both the chemical decomposition and physical phase change is proposed theoretically and verified experimentally. TheF-T p curve of RDX is characteristically distinguished from that of HMX. During the whole pyrolysis process, while both physical vaporization or sublimation and chemical decomposition occur in RDX,only the relatively pure chemical decomposition occurs in HMX.F-T p curves based on easy and simple Py/GC can be used not only for the investigation of chemical decomposition associated with the thermal stability of mate-rials,but also for changes in its physical phase.