2, 3-Dihydro-1H-imidazo[4, 5-b]pyridin-2-one(1) was synthesized by ring-closing reaction using 2, 3-diaminopyridine as primary material. A novel compound 1, 3, 5-trinitro-2, 3-dihydro-1H-imidazo-[4, 5-b]pyridin-2-one(2) was obtained with it by nitration in the system of HNO₃/Ac₂O, with a yield of 44.6%. Their structures were characterized by ¹H NMR, MS and IR, and thermal behavior of compound 2 was studied by differential scanning calorimetry and thermogravimetry. Results show decomposition temperature of compound 2 is 153.0 ℃, and the mass loss due to overall reaction (130~450 ℃) is 55.5%, indicating poor heat stability of compound 2.