Zircon U-Pb dating indicates that the age of the Zhuanshanzi pluton from northwest Linxi County is 245.6±0.9 Ma. The pluton and the Longtoushan and Jianshetun plutons in southeast Inner Mongolia constitute an early Triassic granite belt, which is approximately parallel with the Xar Moron river ophiolite belt. Petrological and geochemical studies indicate that all the plutons are calc-alkaline and high-K calc-alkaline granites and their aluminum saturation indexes (ACNK) are less than 1.1, so they belong to metaluminous or weak peraluminous I-type granite. The fractionation between light and heavy rare earth elements of Zhuanshanzi pluton is weak and the pluton has low Sr content (<400×10-6), which are the characteristics of typical island arc magmatic rocks. The Jianshetun pluton has relatively stronger fractionation between light and heavy rare earth elements and higher Sr content (>400×10-6), which are the characteristics of adakite. While the degree of fractionation between light and heavy rare earth elements and the Sr content of Longtoushan pluton are between those of the former two plutons. The zircons of all the three plutons have positive εHf(t) values. All the geochemical characteristics above indicate that the plutons originated from different degree partial melting of the juvenile lower crust under different depths. Considering regional stratigraphic and magmatic data, it is suggested that the early Triassic granite belt and coeval mafic volcanic rocks in southeast Inner Mongolia were formed in an extensional geodynamic setting during the collisional orogenic process between the Siberian and the Sino-Korean paleoplates, which might have relation with the upwelling of asthensophere caused by the break-off of the southward subducting Paleo-Asian Ocean plate in early Triassic.