The invention provides a thymopentin injection, comprising a thymopentin as an active component, a plurality of accessories for injection, and certain amount of sterile water for injection, wherein the accessories for injection comprises protective agent, antioxidant and pH regulator. The dosage is as follows: point one to two hundred mg/ml thymopentin, ten to two hundred mg/ml protective agent, point one to ten mg/ml antioxidant, and point five to twenty mg/ml pH regulator. The injection has the advantages of stability while refrigerated at the temperature between two to ten degrees centigrade and long periods of preservation; the purity of the thymopentine remains ninety-nine percent after being stored for twenty-four months; the injection can be stored for six months to twelve months at normal temperature, which significantly facilitates circulation and transportation of drugs, thus ensures excellent stability of the injection.