Abstract: A segmental precast composite-material composite-slab composite beam and a construction method thereof are provided, relating to the technical field of bridge design and construction. The segmental precast composite-material composite-slab composite beam mainly includes a segmental precast orthotropic composite top slab, a web, a bottom slab, and a wet joint between segments. The orthotropic composite top slab is composed of an orthotropic slab and an ultra-high-performance concrete layer (UHPC), and the interface connection of the orthotropic slab and the UHPC structural layer is achieved by a shear key. The UHPC structural layer is superposed with the orthotropic slab in segments in a precast plant to form a composite-slab composite beam segment to be entirely transported, hoisted and assembled, and the connection of the UHPC structural layers between the segments is achieved by casting a transverse wet joint in place.