The main product of nitrolysis of 3, 7-dinitro-1, 3, 5.7-tetrazabicyclo[3.3.1]nonane(DPT) in dinitrogen pentoxide/nitric acid/ammonium nitrate with lower dinitrogen pentoxide concentration is HMX. While with higher dinitrogen pentoxide concentration, some of straight-chain by-products of both 1, 9-dinitroxy-2, 4, 6, 8-tetranitro-2, 4, 6, 8-tetrazanonane and N, N′-bis(hydroxymethyl)nitramide were obtained and separated by column chromatography, and the structures were confirmed with infrared spectroscopy(IR), nuclear magnetic resonance(HNMR) and mass spectrometry(MS). Increasing dinitrogen pentoxide concentration leads to more by-products. Nitrolysis of DPT in dinitrogen pentoxide/nitric acid or dinitrogen pentoxide/methylene chloride afforded only straight-chain by-products.