The invention relates to a split mounting type external wall insulated-decorative structural system and a method for mounting the same. The structural system comprises an insulation layer and an external decorative cover layer which are fixed on the external surface of a structural wall body, wherein the external decorative cover layer is slablike and is fixed on the external surface of the structural wall body through a structural supporting system; the insulation layer is filled in the gap between the external decorative cover layer and the external surface of the structural wall body; the structural supporting system comprises I-shaped keels of which the cross sections are I-shaped and which are transversely arranged at intervals and a Z-shaped connecting piece which is provided with connecting holes, wherein one end of each of the Z-shaped connecting piece is fixedly connected with the I-shaped keels while the other end is fixed with the structural wall body through the connectingholes; and the external decorative cover layer is embedded between two I-shaped keels, the two longitudinal edges of which are blocked in the grooves on two sides of the I-shaped keels respectively, and the bottom edges of which are supported on an interspace-adjusting fastener. The split mounting type external wall insulated-decorative structural system adopts the split mounting type so that most of the components are fabricated parts, and has the advantages of various dimensions, beautiful patterns, functions of both external heat preservation and decoration for buildings, energy conservation, high efficiency, beautiful veneer, environmental protection, and convenient construction.