The fully optimized molecular geometries and electronic structures of isomers of 5-amino-3-nitrotriazole [1H-ANTA( (Ⅰ), 2－ANTA(Ⅱ) and 4H-ANTA(Ⅲ) are obtained by using ab initio method at HF/3-21G level and DFT method at B3LYP/ 6-311G^** level based on the potential energies surface scanning at the HF/3-21G and B3LYP/3-21G level, respectively. The accurate energies at MP2/6-311G^**//HF/ 6- 311G^**level and solavtion effects (in tetrahydrofuran) of three isomers have also been obtained. On the bases of the vibrational analysis and statistical thermodynamic theory, the thermodynamic parameters (enthalpies, entropies and heat capacities ) for titled compounds, the equilibrium constants and rate constants of tautomerization of Ⅰ ←→ Ⅱ from 300K to 1000K, were calculated. The results show that Ⅱ is the most stable among three titled compounds in gaseous state at ordinary temperature, and Ⅰis the most stable in liquid phase. The tautomerization reaction Ⅰ ←→ Ⅱis difficult to occur at lower temperature. The tautomerism rate of 1H- ANTA and 2H-ANTA is up when the temperature increasing. Ⅱand Ⅰare equally coexisted in contents at 800K. Ⅰ is more stable than Ⅱat above 800K.

Key words: DYNAMICS, EXPLOSIVES, NITRO GROUP, AMINO GROUP, PYRRODIAZOLE P, AB INITIO CALCULATION, TAUTOMERISM, THERMODYNAMIC PROPERTIES, STABILITY