The nitration process of 3,7-dinitro-1,3,5,7-tetrazabicyclo［3.3.1］nonane (DPT) to 1,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooctane (HMX) was studied using density functional theory at the B3LYP/6-31G** level. Several important factors such as the electron density, bond length, bond order and second-order perturbation energy were calculated. The results show that, because of the influence of bond length and bond dissociation energy, the nitration of DPT not only leads to the intermediate with eightmembered ring but also six-membered ring. Besides that, byproducts would generate in the nitrolysis of the eight-membered ring products to HMX, which was affected by the bond dissociation energies and the secondorder perturbation energy. Therefore, the nitration process is affected both by experiment and molecular structure. Through calculation, the quantum chemical parameters microscopically provide the intrinsic reasonable explanation why the yield of HMX is limited in industrial production.