The synthesis of the 4,5-nitroimidazole with yield of 89.4% was described: the disulfuric imidazole salt obtained from the neutralization of imidazole with concentrated sulfuric acid, was nitrated by mixture of sulfuric acid (20%) and nitric acid (98%) under condition of N₂, and then reacted with nitric acid (98%) at 90-95 ℃ for 5-5.5 h. The conditions for later reaction with nitric acid was discussed at same time. And the results show that the optimal are the molar ratio of nitric acid to imidazole is 1.6∶1, reaction temperature 90-95 ℃, and reaction time 5-5.5 h.