Abstract: The West Kunlun Mountains is the product of the Tarim block and the Qiangtang plots in the Late Mesozoic collision orogeny. The closing time of the Kurdish-Aqiang rift valley is also controversial. In this paper, we studied the petrology, geochemistry and chronology of prophyritic monzonitic granite of the Kudi northern. In this paper, the LA-ICP-MS zircon U-Pb age is 244.42±0.87Ma, and the age is Middle Triassic. The SiO₂ content of the porphyritic granite is 65.57%~67.70%, Mg^#=35~38, A/CNK=.90~1.01, belonging to the aluminum-alkali high-potassium calc-alkaline rock. The total amount of rare earth elements is 193×10^-6~339×10^-6, δEu=0.72~0.78, with weak negative anomaly。Trace elements Rb, K, Th, U, La, Ce, Zr are enriched, Nb, Ti, P medium-strong loss. The porphyritic granite belongs to the I-type granite, and the source rock is the Andesite, which is formed in the subduction continental island arc environment. Regional data, previous achievements and research in this paper indicate that the porphyritic granite was formed in the continental arc environment of the Middle Triassic, and that the ancient Tethys oceanic crust subduction activity existed in the reservoir area of the Middle Triassic, Kulliag-A Rift Valley has not yet reduced closure.