The invention relates to a connecting piece used in building construction, in particular to a connecting tube for connecting and fixing an external wall scaffold and a wall in building construction, which comprises an embedded steel bar, a sleeve, a pulling rod, a gasket, a nut and a connecting rod, wherein one end of the embedded steel bar extends out from the wall, the part, extending out from the wall, has straight threads; the two ends of the pulling rod have straight threads; the sleeve has internal straight threads; the end, extending out from the wall, of the embedded steel bar and one end of the pulling rod are inserted into the sleeve to be fastened; the pulling rod is inserted into the connecting rod; and the other end of the pulling rod is provided with the gasket, and the connecting rod through which the pulling rod passes is fastened by the nut and the pulling rod. In the novel scaffold connecting tube, the sleeve and the embedded steel bar are tightly connected by screw threads and are easy to detach, so risks of overhead work for building a scaffold welded connecting tube on site, the construction speed is improved, the civil construction level is improved and safety is ensured; the thermal-insulation layer of the external wall is guaranteed; and the arrangement of scaffold holes is avoided, and the maintenance problem that the external wall scaffold holes leak after completion and commissioning is solved radically.