The standard enthalpies of formation for 7 derivatives of 4,5-dinitroimidazole in gas at 298 K were determined using isodesmic reactions at B3LYP/6-311G** and B3P86/6-311G** levels. The results indicate that the substitution of nitro group can increase the enthalpies of formation. The more the number of nitro group, the higher the enthalpies of formation. The standard enthalpies of formation of –NO 2 and –CH 3 substitution compounds on N atom are larger than corresponding ones on C atom.