The invention belongs to the technical field of applications of chemical products, and in particular discloses an application of salinomycin in killing external parasites of aquatic animals. The invention aims at providing the novel application of the salinomycin, namely application in killing external parasites of the aquatic animals. The adopted salinomycin is low in toxicity, free from toxins and harm to the aquatic animals and low in residue; a specific dissolving agent and a specific solvent are adopted, so that a good dissolving effect is achieved, and in addition, the dissolving agent can assist insecticides in entering ichthyophthirius multifiliis and cryptocaryon irritans, so that an obvious effect of killing the ichthyophthirius multifiliis and cryptocaryon irritans can be achieved; and the insecticide (the salinomycin) is simple to prepare, convenient to use and low in production cost.