With glyoxal, methylhydrazine and hydroxylamine hydrochloride as starting materials, 2-methyl-4, 5-dinitro-1, 2, 3-triazole-1-oxide(DNMTO) was synthesized by the process of condensation, oxime, cyclization and nitration with yield of 16% and purity of 99%, and title compound and its intermediate were characterized by IR, ¹H NMR and elemental analysis. Compared with the four-step reaction in the literature, this approach was reduced to two steps. The optimum conditions for the cyclization and nitration reaction were as follows: reaction temperature was 100 ℃ and reaction time was 0.5 h. The structure of DNMTO was also estimated by a B3LYP method based on aug-cc-pVDZ basis set and the stable geometric configuration and bond order were obtained. The relationships between temperature and thermodynamics properties were confirmed. The results show that all thermal energy, thermal capacity and entropy increase with the increase of temperature.