Abstract: There are large-scale intermediate-acid intrusive rocks distributed in the north of western Junggar, Xinjiang. The rocks formed during late Carboniferous to early Permian. The typical plutons include pyroxene diorite, quartz diorite and granodiorite. The Kuoyitasi intrusion is among one of them. It has SiO₂ values of 52.40%-67.53%, high Al₂O₃ content (14.92%-17.85%) and Na content, and low K and MgO content. Rittman values (δ) of the samples vary from 1.47 to 1.98, and the FeO^T/MgO values are between 1.01 and 1.69. The REE patterns are characterized by LREE enrichment and slight Eu anomalies with obvious fractionation between LREE and HREE. The geochemical characteristics suggest that the Kuoyitasi intrusion formed in a post-collisional extensional tectonic environment, and should be formed earlier than the collision time of east Junggar terrain. The rocks were probably derived from partial melting of the lower crust which was intruded by mafic magmas.