A protecting cap structure of a charging gun has a cover, a push plate, a fixing seat, at least one first resilient element, and a gland. The push plate is moveably mounted in a containing groove of the cover. The fixing seat, the first resilient element, and the gland are mounted in the containing groove. The first resilient element and the gland are respectively mounted on both sides of the push plate, and the first resilient element abuts and pushes the front side of the push plate. The protecting cap structure not only improves water resistance and dust resistance by the gland which is propped by the resilient element when the cover covers the plug of the charging gun, but also is easy to use because the resilient elements push forward the cover when the cover is to be removed.