Provided are a box-type roadbed structure of a high-speed rail and a construction method. The structure and the method aim to effectively reduce the building cost of a high-speed rail roadbed in a flat area and reduce roadbed land maximumly. Reinforced-concrete box-type body segments are arranged on the roadbed in the track direction continuously, expansion joints are arranged between the end surfaces of the adjacent reinforced-concrete box-type body segments, the reinforced-concrete box-type body segments are formed by integrally solidifying baseboards, left side vertical arm walls, right side vertical arm walls and top boards and form a box-type cross section, and the top boards of the reinforced-concrete box-type body segments are the basis of a track system.