Abstract: An insulating sheath of a plug has a sheet-like sheath main body (1), a contact pin sheath (2) and a contact pin hole (3). The contact pin sheath protrudes from the sheath main body, the contact pin hole is a through-hole allowing the contact pin sheath to communicate with the sheath main body, and the contact pin hole is used for being sheathed on a contact pin of the plug. The insulating sheath can adhere the sheath main body to an insulation part of the plug, and can protect the contact pin at the same time, preventing short circuit by water leakage or electric leakage between contact pins, and also preventing an electric shock caused by a finger touching the contact pin without affecting normal plugging-in and unplugging of the plug.