The invention discloses a preparation method of natto red yeast rice health care food for assisting in lowering blood lipid. The preparation method is characterized in that soybeans serves as the raw material and is soaked, steamed and boiled, cooled, inoculated with bacillus natto, fermented, refrigerated, frozen, dried, crushed and processed into natto powder, then red yeast rice extract and magnesium stearate are added, then the ingredients are mixed to be prepared into granules or capsules, and the natto red yeast rice health care food is prepared from, by weight, 50-70% of the natto powder, 30-50 parts of the red yeast rice extract and 0-3% of magnesium stearate. According to the preparation method, adopted raw material components are scientific in compatibility, the adopted technological process and method are reasonable, scientific and easy to operate, the obtained product is free of toxic and side effects, capable of being easily absorbed by a human body and convenient to eat, it is beneficial to prevent and control atherosclerosis hardening of the arteries and lower the risk of cardiovascular diseases, and the health care function of assisting in lowering blood lipid is achieved.