Abstract: The Xinyuan volcanic rocks in western Tianshan mountains mainly consist of basahs，basaltic trachyandesites，trachyandesites，andesites，rhyolites and pyroclastic materials．The basahs constitute calcalkaline association，whilst the andesitic rocks and rhyolites belong to high-K calcalkaline series．The REE patterns indicate thatLREES are slightly enriched and HREES are comparatively depleted in the studied volcanic rocks．In the primitive mantle-normalized trace element diagrams， basahs show LILE， U，Th and Pb enriched patterns with HFSE troughs．This study displays that the volcanic magma probably came from the partial melting of the mantle wedge，which had undergone metasomatism induced by the subduction fluid．According to calculation，3 to 6 percent partial melting of garnetlherzolite could produce the basalt magma．The andesitic magma could be produced by the fractional crystallization of basalt magma，the fraction of which is 15 to 28 percent.