Two simultaneous devices, the rapid thermolysis reaction cell (gas reaction cell) in situ in conjuncton with rapid-scan Fourier transform infrared spectroscopy (RSFT-IR),and the solid reaction cell in situ with RSFT-IR, are constructed for measuring the gas products and condensed phase products of thermal decomposition of nitrocellulose (NC) in real time. Two methods for determining the above mentioned products are presented. Under linear temperature increase condition,the thermal decomposition reaction of NC are experimentally studied, and a mechanism for this reaction is proposed based on the results.