Disclosed is a composition for promoting local muscle growth or slowing down or preventing local muscle atrophy, which composition contains a polypeptide in the C2 region of the enterotoxin Staphylococcus aureus and a myostatin polypeptide. By means of the composition, the defect in the prior art of only systemic muscle growth being possible has been overcome so as to achieve effects of promoting local muscle growth, or slowing down or preventing local muscle atrophy.