Abstract: Lithology, LA-ICP-MS zircon U-Pb age, and geochemistry of coarse grained porphyaceous monzonitic granite from Lower Cretaceous Cuolong Co area in the west of the middle Gangdise granitoid belt were studied in detail in this paper. The results show that magma zircons from coarse grained porphyaceous monzonitic granite yielded a weighted mean age of 212.6±2.7Ma, indicating Late Triassic. The rock is shoshonitic or high K calc-alkaline and relatively rich in Si₂ and K₂O. Al₂O₃ content is between 13.18% and 16.26%, A/CNK ratios vary from 0.96 to 1.33 (1.11 on average), displaying peraluminous characteristics. Total rare earth element values are between 182.99×10^-6 and 324.34×10^-6. Trace element ratio spider diagram displays apparent enrichment of light rare earth elements, depletion of heavy rare earth elements, δEu variation between 0.38 and 0.57, and sharp negative Eu anomalies. Trace elements are characterized by enrichment of K, Rb, Th and depletion of Ba, Nb, Sr, P, Ti, similar to features of orogenesis granite. Geodynamic analysis of rock background shows that it was most likely associated with a back-arc setting in response to conversion from compression to stretching related to the southward subduction of the Bangong Co-Nujiang oceanic lithosphere.