The invention discloses a synthesis method of trinitrobenzo [4, 5] imidazo [2, 1-c] [1, 2, 4] 
triazine-4-one, and the method comprises the following steps: adding concentrated 
sulfuric acid into a reaction flask at low temperature, adding 3-nitro-4-amino-benzo [4, 5] imidazo [2, 1-c] [1, 2, 4] 
triazine in batches, and stirring; dropwise adding fuming 
nitric acid, heating to obtain a first reactionsystem after the reaction is finished, pouring the first 
reaction system into 
ice water, extracting a water phase by using 
ethyl acetate, combining organic phases, 
drying with 
anhydrous sodium sulfate, concentrating the organic phases to obtain a crude product, and further purifying the crude product through 
column chromatography to obtain 3, 7, 9-trinitrobenzo [4, 5] imidazo [2, 1-C] [1, 2, 4] 
triazine-4 (3H)-one and 3, 9-dinitrobenzo [4, 5] imidazo [2, 1-C] [1, 2, 4] triazine-4 (3H)-one. The 
raw material 2-aminobenzimidazole used in the reaction is a commercialized product in the market, and is low in price and easy to obtain.