The intermediate 1,4-formaldehyde-2,3,5,6-tetrahydroxy-piperazine (DFTHP) was prepared by the reaction of formamide and glyoxal condensed in alkaline condition, then it was condensed and nitrified in the system of heteropolyacid/pure nitric acid to obtain 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diaza-tetracyclo dodecane (TEX). TEX was characterized by infrared spectroscopy and nuclear magnetic resonance spectroscopy, and the mechanism of the reaction was also discussed. H₃[P(W₃O₁₀)₄] was proved to be the favorable heteropolyacid catalyst, the optimum processing conditions were determined as: mass ratio m(DFTHP)/m(urea)=1:0.25, the dosage of H₃[P(W₃O₁₀)₄] 1 g, adding the reactants at 50 ℃, reaction temperature 65 ℃ and reaction time 40 min, with the yield of TEX 44.7%.