This paper studys in the Yaergenchu granites in northern Da Hinggan Range. The granites consist of syenogranite, mylonitized granite in lithology. Using zircon U-Pb LA-ICP-MS dating method , with the results of concordant ages of 226.8±2.2Ma、230.2±1.3Ma and 233.6±1.5Ma, indicating intrusive time of the granites is the late Triassic. The chemical analyses show that the granites have high SiO2, K2O contents, A/CNK ratios ranging from 0.81to 1.10. The REE patterns are characterized by enrichment of LREEs relative to HREEs with negative Eu anomalies in chondrite-normalized REE diagram. The trace elements are relatively enrichment of large ion lithophile elements (LILE), depletion of high field strength elements (HFSE). These features are similar to the island arc granites and I type granites. Through integrated study, we think these I type granites were formed in the whole extensional setting. With the decreasing of the pressure in lithosphere mantle, it caused the upwelling of the mantle, than the residual oceanic crust molten which caused the emplacement of this pluton.