The invention discloses a closure segment formwork system without dismantling an outer formwork. The closure segment formwork system without dismantling the outer formwork comprises a bottom formwork, the outer side formwork and an inner side formwork; embedded parts are embedded in the ends of cantilever segments of a poured bridge, the bottom formwork and the outer side formwork are fixed on the embedded parts through outer side formwork frameworks, and the inner side formwork is supported in the inner side of a web plate and a base plate of the ends of the cantilever segments of the bridge through inner formwork supports; the bottom formwork, the outer side formwork and the outer side formwork frameworks are within the design contour line of the bridge. After the construction is completed, the bottom formwork, the outer side formwork and the outer side formwork frameworks become one part of a permanent structure of the bridge. A pull rod is not arranged between the inner side formwork and the outer side formwork. The bridge closure segment construction can be achieved on the condition that the safe distance between a proposed bridge and existing buildings such as high-voltage cables under the proposed bridge are limited.