The present invention provides a dust-proof adapter comprising an adapter body, a flexible element, and a cap, wherein the adapter body has an opening at a coupling side and a ring-shaped surface surrounding the first opening, the flexible element is arranged onto the ring-shaped surface, and the cap detachably covers the adapter body for protecting the first opening. When the cap is covered on the first opening, the cap applies an action force along an axial direction of the adapter body on the flexible element thereby achieving air-tight and dust-proof effect.