The invention discloses a cast-in-cantilever structure of a movable crane formwork of a zigzag-form steel web continuous box beam and a construction method of the cast-in-cantilever structure, and relates to the field of a cast-in-cantilever construction method of zigzag-form steel web continuous box beams. The cast-in-cantilever structure mainly comprises a cast-in-cantilever construction movable formwork, a movable crane, piers, bent frames, cast-in-cantilever beam sub blocks and the like, wherein the zigzag-form steel web continuous box beam is formed by the piers, the bent frames, the cast-in-cantilever beam sub blocks and the like, and all the cast-in-cantilever beam sub blocks are sequentially subjected to cast-in-cantilever construction by matching the movable crane with the cast-in-cantilever construction movable formwork, so that cast-in-cantilever construction of the zigzag-form steel web continuous box beam is formed. The cast-in-cantilever structure disclosed by the invention is simple in construction and convenient to use, is capable of providing three working surfaces to carry out asynchronous cast-in-cantilever construction on the zigzag-form steel web continuous box beam and has the construction advantages of safety, reliability, remarkable benefit and the like after a corresponding construction method is combined.