The invention discloses a preparation method of high-nutrition coarse cereal bread flour. On the premise of ensuring the proper wet gluten content, water content and good processing characteristics ofthe coarse cereal bread flour, the processing properties of the coarse cereal flour such as catalytic yeast fermentation, foaming, coagulation and the like and the baking quality can be improved without adding flour modifiers such as potassium bromate, azodicarbonamide and the like, and meanwhile, the content of dietary fibers in the bread flour is increased; according to the characteristics of raw materials, different processes such as enzymolysis combined with ultrasonic extraction and the like are adopted, so that nutritional ingredients in the bread flour are properly decomposed, the digestibility is improved, and the nutritional degree is high; corresponding raw materials are premixed while being conveyed in a conveying pipe through a conveying auger, and the corresponding raw materials in a grinding cylinder are ground through three grinding rollers; and meanwhile, through the design of an airflow classifier, the raw materials are mixed and ground in a low-temperature environment, and the grinding efficiency is high.