1-Methyl-3,5-dininitro-1,2,4-triazole (MDNT) was synthesized from hydrazine dihydrochloride and cyanoguanidine via a three step procedure (condensation cyclization,diazotization nitration,and methylation). The total yield is 16.75%,melting point is 95-96 ℃，and purity is more than 99% for the purified MDNT. The structure of the obtained MDNT was characterized by ¹H NMR,IR and elemental analysis. The extraction of 3,5-diamino-1,2,4-triazole (DAT) by hot methanol improved DAT′s yield from 89.0% to 96.5%. The thermal decomposition of MDNT proceeds in two stages. The corresponding peak temperature is 95.7 ℃ and 230.2 ℃,and decomposition heat is 16.505 kJ·mol^-1and 112.582 kJ·mol^-1,respectively.