The invention discloses a method for preparing ancient-prescription brown sugar with a menstruation regulating action. The method comprises the procedures of firstly, juicing sugar canes, carrying out filtration so as to remove bagasse, adding a drug bag into sugar-cane juice, carrying out series pot decocting, carrying out scattering, carrying out mold loading, carrying out cooling molding, carrying out air drying, carrying out bundling-up by sugarcane leaves, carrying out secondary air drying, and the like. The drug bag is prepared from the following ingredients in parts by weight: 1-10 parts of folium artemisiae argyi, 5-15 parts of herba leonuri, 1-10 parts of zingiber officinalis, 1-10 parts of Chinese angelica, 1-10 parts of prepared rehmannia roots, 1-10 parts of rhizoma chuanxiong, 5-15 parts of radix paeoniae alba and 5-15 parts of dried red dates. According to the method, series-pot manual decocting is used, the method is a pure physical method, no chemical additive is added, and normal-temperature natural crystallization is carried out, so that a variety of nutrients such as glucose, brown sugar, amino acids, nicotinic acid and carotene in the sugar canes are naturally reserved, the taste is naturally fragrant and sweet, the sandy feeling is rich, the ancient-prescription brown sugar is melted once the ancient-prescription brown sugar enters a mouth, and the ancient-prescription brown sugar is agreeable in sweetness. The ancient-prescription brown sugar has the effects of nourishing Yin and tonifying blood, removing heat from the liver, regulating and nourishing Qi and blood, activating blood circulation to dissipate blood stasis and promoting circulation of Qi to relieve pain and is good in effect and high in effect taking speed.