The invention relates to a building wall insulation composite board and a preparation method of the building wall insulation composite board, and belongs to the technical field of building energy-saving insulation materials and preparation methods. A wall insulation hard foam polyurethane composite board comprises inner cores, protective layers coated on the peripheries of the inner cores and interface layers coated on the upper surfaces and the lower surfaces of the protective layers in an attached mode. The inner cores are vacuum insulation boards. The preparation method of the wall insulation hard foam polyurethane composite board comprises preparation of interface coiled materials: coating prepared flame-retarded polymer mucilage on base materials to produce the interface coiled materials, and manufacturing of the protective layers and the wall insulation hard foam polyurethane composite board. The insulation composite board has good thermal insulation performance, waterproof performance and heat insulation performance, can satisfy 65% requirements of building energy efficiency very well, is high in bonding strength and convenient to construct and operate, greatly increases overall fireproof performance of the whole wall heat-insulation system after being arranged on a wall, and can be widely applied to the inner portions of walls, outer walls, and roof covering thermal insulation systems, heat insulation systems and waterproof systems.