The invention relates to a cylindrical foundation water gate structure and a construction method for a closure of a cofferdam. The cylindrical foundation water gate structure comprises a cylindrical foundation, and is characterized in that an upper water gate structure is arranged on the upper portion of the cylindrical foundation and comprises an upper toe wall, a lower toe wall at the upper end of a cover plate, gate grooves, longitudinal walls, gates and panels; the cover plate of the cylindrical foundation is fixedly connected with the lower toe wall at the upper end of the cover plate; the lower toe wall at the upper end of the cover plate is fixedly connected with the gate grooves; the gate grooves are fixedly connected with the upper toe wall; the upper toe wall is provided with a through groove; the gates penetrate in the through groove and are inserted in the gate grooves; the adjacent gate grooves are connected to one another through the longitudinal walls along the longitudinal axis direction; and the panels are arranged at the upper end of the upper toe wall and the upper ends of the longitudinal walls. The cylindrical foundation water gate structure has the advantages that the cylindrical foundation is used, so that pouring or installation of the water gate structure is performed above water; construction of a cofferdam project is then performed step by step; and the troublesome process of underwater pouring is avoided.