A cast water-cooled high-frequency transformer casing structure and a manufacturing method thereof, wherein the casing comprises an upper casing and a lower casing; The upper shell and the lower shellare all provided with a semi-cylinder in the middle part, and a semi-circle penetrating the semi-cylinder is arranged beside the rectangular surface of the semi-cylinder; The axial surface of the semi-cylinder is provided with a cylindrical through hole; An annular inner cavity is arranged outside the semi-cylindrical and semi-circular holes of the outer shell; A groove is provided on the edge ofthe inner cavity of the; A waterway is provided in the interior of the enclosure. A manufacture method comprises that follow five steps of: processing a shell core mold, processing waterway mold sand, placing waterway mold sand, and performing casting. The outer shape of transformer shell, the installation cavity of transformer primary coil and its cooling water channel, fixed hole are cast once,which reduces the workload of machining in the later stage and greatly improves the production efficiency. The water channel inside the transformer casing is over-arc, which can effectively reduce the movement resistance of water flow and increase the cooling efficiency.