The invention relates to a building member, in particular to a complex heat-preservation roof and a construction method thereof. The roof comprises a roof truss, EPS boards and waterproof boards, the multiple EPS boards are arranged between purlins of the roof truss, and the waterproof boards are arranged on the EPS boards and the purlins; and the two end surfaces of the roof truss are also provided with the waterproof boards. The construction method is as follows: the EPS boards are arranged on the roof truss, the upper surface of each EPS board and the upper surfaces of the purlins are coplanar; reflecting films are stuck on the upper surfaces of the purlins and the EPS boards; the waterproof boards are assembled on the two sides of the lowest end of the roof truss, and then are paved on the previous layer until the surface of the roof truss is completely paved; a baffle is arranged on the roof truss and is provided with a first bracket, the first bracket is provided with an external pinchplate, and a drain tank is arranged on the first bracket by the external pinchplate; a second bracket is arranged below the first bracket, and a perforated plate is arranged on the second bracket; and the waterproof boards are used to seal the two end surfaces o the roof truss. The invention has the advantages of environment protection, heat preservation, thermal insulation, sound insulation, convenient installation and the like.