The invention relates to a method for extracting chlorophyll iron-chromium salt from an alga. The method is characterized by comprising the following steps: (1) cleaning, drying and pulverizing the alga; (2) extracting the alga in an aqueous solution of an organic solvent; (3) carrying out extraction to obtain chlorophyll through a centrifuge and performing vacuum filtration; (4) slowly adding chromic chloride hexahydrate into the filtrate from the step (3), and allowing chlorophyll to fully react with chromic chloride hexahydrate; (5) adjusting PH to a range of 3-4, adding a ferrous sulphate solution, and performing sufficient stirring, filtering, and washing to obtain precipitate; and (6) refrigerating the precipitated liquid at a temperature of 5-6 DEG C. According to the invention, a chlorophyll derivative of chlorophyll iron-chromium salt is prepared, and the method is simple and fast, is low in cost and high in purification rate, and has a bright application prospect in food and medicine fields.