Thermal dynamic process of single pulse laser-induced reaction is theoretically analyzed for a novel system of composite energetic materials containing nanometallic particles. The instantaneous power density of laser energy absorbed by nanometallic particles dispersed in a matrix is exactly deduced. The process of absorbing pulse laser energy for nanometallic aluminum particles embedded in nitrocellulose (Al/NC) thin film and the heat propagation process of hot spot accompanying exothermic chemical reaction are simulated numerically based on thermal decomposition mechanism. The reaction diameters are calculated for different concentrations of Al/NC thin films flashed by 100ps, 10ns and 25ns single pulse laser with the reaction threshold intensities having been obtained from experiment, respectively. Calculation results are compared with the experiment data, which shows that the thermal decomposition mechanism generally corresponds to the reaction processes of 10ns and 25ns pulse laser but does not correspond to that of the 100ps pulse laser.