Abstract: The geochemical characteristics of the Lower Jurassic volcanic rocks on the western margin of the Junggar Basin were analyzed. The main, trace and rare earth element data indicate that the rocks are alkaline basalts, enriched with light rare earth elements, large ion lithophile elements and high field strength elements. The trace elements show an ocean island basalt (OIB) distribution model. The basalt magma came from the depleted mantle that was not obviously contaminated by crust, and has the characteristics of continental intraplate rift volcanic rocks related to mantle plume activity. The Tubo-Hami, Dunhuang and other basins in the northwest developed Jurassic basalt of similar genesis with the western Junggar Basin. The basalt formation was related to the rising of regional asthenosphere interface and the thinning of lithosphere, providing dynamic conditions for the formation of extension basin during the early and middle Jurassic. The extension of the Jurassic basin took place earlier in the west and the south, which explained the difference of source rock distribution and hydrocarbon accumulation in the basin.