An extending base for a portable computer is provided. The extending base includes: a base body, an electrical connector fixedly mounted on the base body for being electrically connected with the portable computer, a detachable cover covering the base body for supporting the portable computer, wherein the electrical connector is protrudent out of the detachable cover, a plurality of first engaging elements mounted on the detachable cover, a sliding structure mounted on the base body for sliding along a direction in response to an external force, and a plurality of second engaging elements mounted on the sliding structure for engaging with the first engaging elements so as to fix the detachable cover on the base body.