Located in Shangqimugan area of Akto County in Xinjiang,Shangqimugan plutons exhibit NW-SE trending zonal distribution along the Qiaolakeke-Sugaite-Ajiaerdong fracture. The plutons are mainly composed of monzonitic granite. The SiO₂ values range from 66.06% to 75.13% and Al₂O₃ from 12.45% to 14.78%. Average (K₂O+Na₂O) value is 8.82%, average K₂O/Na₂O ratio is 1.25, and aluminum index A/CNK (0.89～0.98)<1.1,suggesting that the plutons belong to high-K metaluminous calcic-alkaline series. The total REE values of the plutons are 231×10^-6～404×10^-6,and LREE and HREE show obvious fractionation. Chondrite-normalized REE patterns are of smoothly right-oblique type. Average value of δEu is 0.17, implying obvious depletion of Eu. Compatible elements (Ni, Co, Cr, V), incompatible elements (Rb, Th) and HFSE (Zr, Hf, etc.) are obviously concentrated; Ba, Sr, P and Ti are strongly impoverished; Nb and Ta are depleted in a certain extent. LA-ICP-MS zircon U-Pb dating yielded a ²⁰⁶Pb/²³⁸U weighted mean age of 225.4±1.9 Ma (MSWD=6.0), indicating that the plutons belong to early Late Triassic. Combined with geochemical characteristics and trace elements discrimination diagrams, the authors hold that the rocks resulted from the mixing of the crust and mantle magmas, belonged to A-type granite and formed in the tensional environment of a post-collision extensional phase, which marked the end of the orogeny of the West Kunlun orogenic belt and the beginning of intraplate tectonic evolution in early Late Triassic, implying a transition from the collision environment to the intraplate extensional environment. These data also demonstrate the complete closure of Paleo-Tethys in this region in early Late Triassic.