Abstract: The monzonitic granite pluton is located in the Xing'an block, southern Da Hinggan Mountains. The rocks are composed of fine-grained porphyry monzonitic granite and fine-medium-grained monzonitic granite. The zircon U-Pb ages are 141.2±1.6 Ma and 134.0±1.9 Ma, indicating that they are the product of magmatic activity in the Early Cretaceous. Their geochemical characteristics suggest that they are highly differentiated I-type granites of high potassium calc-alkaline series. They are rich in large ion lithophile elements, such as Rb, Th, K and light rare earth elements (LREE), and strongly depleted in Ba, Sr, P and Ti elements. These features are similar to geochemical characteristics of crustal granite.They were formed in a post-collision extensional environment and serve as a magmatic record of the subduction of the Paleo-Pacific Plate.