Abstract: Kalagailei copper-gold deposit, located in the western Nalati tectonic belt of Western Tianshan Mountains, Xinjiang, is the first Cu-dominated volcanic hydrothermal deposit accompanied by Au and Co etc. in this metallogenic belt. The hydrogen and oxygen isotope compositions show that ore-forming fluids were mainly made up of magmatic water in the early period and added by rainwater in the later period. The characteristics of sulfur isotope show that the sulfur sources originate from the deeper crust and upper mantle, accompanying with the interfusion of strata sulfur. The lead isotope compositions indicate that lead sources are mixture of crust and mantle. The Re-Os isotopic model age of molybdenite is (259.6±9.7) Ma, indicating that early stage mineralization age of the deposit falls into the mid-late Permian. The authors probe into the genesis and consider the volcanic rocks of Dahalajunshan Formation are the source beds. At the collision-extensional stage of late Carboniferous, mineral-enriched magmatic hydrothermal fluids originating from the deep crust migrate through regional and large faults, volcanic vents and shallow faults system, and extract early mineral elements, forming the orebody in the favorable tectonic positions.