Abstract: "Structural complex"-an assemblage or mixture of rocks of two or more genetic classes-is very important for tectonostratigraphic research in erogenic belts. In West Junggar of northern Xinjiang, three complexes of different ages were distinguished. They are the middle-late Ordovician or earliest Silurian Kekeshayi Complex, late Silurian Mayile Complex and late Carboniferous Dalabut Complex. However, assemblage of the rock types and tectonic settings of these three complexes are very similar. All are mixture of ophiolitic rocks, pelagic pelitic sediments and clastic turbidites relating to volcanic arcs. This means that in the wide area of ancient central Asia the complicated environment for oceanic basins along with volcanic island arcs lasted a long period from Ordovician to Carboniferous. Intra-oceanic subduc-tion occurred and these complexes represent the remnants of intra-arc, fore-arc or back-arc terranes of different ages. Today’s West Junggar may be composed of many displaced terranes.