A manufacturing method for an outer covering edge of a molded cup lid, with a semi-finished product of the molded cup lid made of a plant fiber material being manufactured by a pulp-shaping process and a heat-pressure shaping process, and the method comprising the steps of: covering an outer mold onto the semi-finished product, and the outer mold having a side profile matching the semi-finished product, and the outer mold having a plurality of slide blocks disposed at a position of the semi-finished product where the outer covering edge is formed and the slide blocks being pushed forward to form an annular body, and a receiving groove being formed on an inner edge of the slide block and with a profile corresponsive to the outer covering edge for moving the slide blocks forward, so as to make the receiving groove to reach an outer surface of the semi-finished product at a position where the outer covering edge is formed; installing an inner mold into the semi-finished product, and the inner mold having a profile matching the profile of the semi-finished product, and a transversally movable shaping mold being installed in the middle of the inner mold, and the shaping mold having a front end formed into a shaping ridge corresponsive to profile of the pre-formed outer covering edge and an external power being installed at a rear end of the shaping mold for driving the shaping mold to move forward or backward, such that the external power may push the shaping mold to move forward to an inner surface of the semi-finished product at a position where the outer covering edge is pre-formed; pushing the shaping mold to move continuously forward by the external power, so that the surface of the semi-finished product is compressed by the shaping ridge and deformed to form the profile of the outer covering edge that enters and remains in the receiving groove; producing a relative rotation between the inner mold with the shaping mold jointly and the outer mold, the slide block and the semi-finished product, and the shaping ridge of the shaping mold being compressed at the inner surface of the semi-finished product and deformed to form an outer covering edge that enters and remains in the receiving groove; and withdrawing the shaping mold to its original position by the external power, while withdrawing the slide block outward, and opening the outer mold and the inner mold to produce the molded cup lid. covering an outer mold onto the semi-finished product, and the outer mold having a side profile matching the semi-finished product, and the outer mold having a plurality of slide blocks disposed at a position of the semi-finished product where the outer covering edge is formed and the slide blocks being pushed forward to form an annular body, and a receiving groove being formed on an inner edge of the slide block and with a profile corresponsive to the outer covering edge for moving the slide blocks forward, so as to make the receiving groove to reach an outer surface of the semi-finished product at a position where the outer covering edge is formed; installing an inner mold into the semi-finished product, and the inner mold having a profile matching the profile of the semi-finished product, and a transversally movable shaping mold being installed in the middle of the inner mold, and the shaping mold having a front end formed into a shaping ridge corresponsive to profile of the pre-formed outer covering edge and an external power being installed at a rear end of the shaping mold for driving the shaping mold to move forward or backward, such that the external power may push the shaping mold to move forward to an inner surface of the semi-finished product at a position where the outer covering edge is pre-formed; pushing the shaping mold to move continuously forward by the external power, so that the surface of the semi-finished product is compressed by the shaping ridge and deformed to form the profile of the outer covering edge that enters and remains in the receiving groove; producing a relative rotation between the inner mold with the shaping mold jointly and the outer mold, the slide block and the semi-finished product, and the shaping ridge of the shaping mold being compressed at the inner surface of the semi-finished product and deformed to form an outer covering edge that enters and remains in the receiving groove; and withdrawing the shaping mold to its original position by the external power, while withdrawing the slide block outward, and opening the outer mold and the inner mold to produce the molded cup lid.