The invention provides a yarn dyeing method, and belongs to the technical field of textile related equipment. The technical problems that for an existing dyeing method, the dyeing efficiency is low, and dyeing is inconvenient are solved. The yarn dyeing method comprises the steps of 1, yarn preparation and inspection, wherein the yarn quality is inspected before yarn dyeing is conducted, and it is required that the appearance of yarns is clean and free of stain, the yarns are neutral, the stacking time must not be over 8 h, and the yarns are covered with wet cloth; 2, feeding, wherein yarns are put into a dye vat and arranged on a yarn dyeing rod; 3, dye preparation, wherein anthraquinone vat dye is prepared in a dye barrel, 5 g-6 g of caustic soda and 5-6 g of rongalite are added according to each part by mass of raw material with an anthraquinone type structure, water is injected to obtain a solution, and 0.2 g / L-0.5 g / L of bone glue retarding agent is added; 4, dye injection and dyeing, wherein the prepared dye is injected into the dye vat; 5, yarn taking-out. The yarn dyeing method has the advantages of being high in dyeing efficiency and uniform in dyeing, and the yarns subjected to dyeing is fluffy and full in hand feeling.