The Kuoshibulak granites located in the northwestern margin of the Tarim Basin are high-K calc-alkaline series,and rich in alkali (Na2O+K2O averages 8.36%>8%)and (K2O/Na2O=1.27~1.47),with the A/CNK values between 0.82 and 0.88,which fall into the range of metaluminous rocks. The geochemical features of the rocks are similar to that of A-type granites. Rb-Th richment,Ti-depletion and the elemental ratios of the Kuoshibulak granites,such as the Th/U (averages 3.86),Nb/Ta (averages 12.75) indicate that it probably derived from crustal source. The Kuoshibulak A-type granites also suggested that the collisional orogeny in the southwestern Tianshan probably finished before (275.4±2.8) Ma,and the paleo-Asia ocean represented by the southern Tianshan ocean is closed at that time.