The invention provides a silver ion cotton yarn dyeing method, and relates to the field of antibacterial fabric dyeing. The method comprises the following steps that S2, a hydrogen peroxide stabilizing agent and a metal sealing agent are stirred with water flow evenly, then sodium carbonate and hydrogen peroxide are added to perform bleaching desizing treatment, the operation is carried out for 60minutes after the temperature rises to 80 DEG C; the bleaching desizing treatment is carried out on the cotton yarn through the sodium carbonate and the hydrogen peroxide; in the desizing process, the addition of the sodium carbonate takes the place of caustic soda, the sodium carbonate molecule is Na2CO3, the water solution of the sodium carbonate is 11.6 and less than that of the caustic soda,so that it is avoided that the whiteness of the cotton yarn is reduced and broken holes occur in the fabric due to that the pH value exceeds the hydrogen peroxide stable decomposition range during thedesizing process; redundant pigment, resin and other foreign matters adhered to the surface of the cotton yarn is removed through multiple times of soaping, and the cleanliness of the cotton yarn isensured.