The utility model belongs to the field of a building barrier material, in particular to a separator for a building external wall. The separator comprises an outer plate, a middle interlayer and an inner plate, wherein the outer plate is internally provided with a plurality of hollow spherical shells, the outer plate is 2-2.5cm, the middle interlayer is provided with a plurality of round bars arranged in parallel and is 1.5-2cm thick; fireproof asbestos are filled among the round bars, the inner plate is internally provided with a plurality of sealed air bags and is 1.5-2.5cm thick, the sealed air bags are uniformly arranged in the inner plate, and the round bars are internally hollow. According to the built-in hollow spherical shells provided by the utility model, the outside noise can be isolated highly; furthermore, by adopting the combination of the sealed air bags filled with carbon dioxide and the fireproof asbestos, the spreading of open fire can be effectively prevented; in addition, by adopting a three-layer structure, the separator is filled with the asbestos, therefore the heat-preservation and heat-insulation effects are good.