1-Methyl-4,5-dinitroimidazole(4,5-MDNI) was synthesized from nitration of 1-methylimidazole. 4,5-Dinitroimidazole (4,5-DNI) displaying acidity was dissolved. The structure of 4,5-MDNI was characterized by IR,elemental analysis,1H NMR and MS. Effects of the temperature, reaction time and the ratios of fuming sulfuric acid to fuming nitric acid on its yield were studied by orthogonal test. The optimal reaction conditions for synthesizing 4,5-MDNI are obtained as follows: the yield of 4,5-MDNI is 60%, and reaction temperature is 105-115 ℃, and reaction time is 2 h, and the ratios of sulfuric acid and nitric acid is 1：1. The thermolysis property of 4,5-MDNI was studied by differential scanning calorimetry(DSC). Results show that the melting point of 4,5-MDNI is 78 ℃,and 4,5-MDNI has good thermal stability.