The invention discloses a formula and a preparation method of beans capable of blackening hair, which are characterized in that: black beans serve as main raw materials, and are prepared into 'bean food capable of blackening the hair' by using a scientific formula and preparation method for the preparation of polygonum multiflorum, unprocessed rehmannia root, black sesame, fructus ligustri lucidi, dried oriental arborvitae, eclipta alba, green salt, pericarpium zanthoxyli, dried tangerine peel, angelica sinensis, ligusticum wallichii, eucommia ulmoides, liquorice, radix paeoniae alba, rhizoma atractylodis macrocephalae, chrysanthemum, fried astragalus mongholicus, twotooth achyranthes root, rehmannia glutinosa, barbary wolfberry fruit and the like; therefore, the 'beans capable of blackening the hair' has the functions of tonifying liver and kidney, benefiting the energy and blood, and blackening beard and hair, and are suitable for treating symptoms of deficiency in liver, kidney and blood, early graying hair, hair shedding and the like; the often taking of the 'beans capable of blackening the hair' is beneficial for a person in gray hair to grow black hair; moreover, the beans do not lead to the hair shedding, and has the advantages of protecting and beautifying the hair. The elimination of allergy, toxicosis, skin cancer and the like of skin of the head due to poisonous and harmful substance such as chemical hair colorant and the like is realized.