5, 6 - Dimethylbenzimidazole is an important early raw material for the synthesis of vitamin B12.The synthetic route was using 3, 4 - dimethyl aniline as raw material, through acylation, nitration, hydrolysis, reduction, cyclization, five-step reactions, the total yield was about 40%. In order to improve the product yield and quality, the nitration reaction was mainly studied. The important technology indicators that affect nitration reaction were nitration reaction temperature, time and nitrating agent dosage of moles. Through research on 5, 6 - dimethylbenzimidazole nitration process, the best nitration reaction conditions were that reaction temperature was 30 ～ 45 ℃, reaction time was 30 minutes, and the amount of nitrating agent was 1.6 times of the theoretical molar weight,the overall yield of five-step reactions could be as high as 50.3%.