The Muztagata pluton is the largest granitic intrusion in Western Kunlun orogenic belt, which is composed of biotite monzonitic granite, porphyritic like biotite monzonitic granite and granodiorite with a mass of widely developed dark microgranular enclaves and basaltic magmatic stripes. Noticed that the zircons of the rocks are typically magmatic zircon according to their cathodoluminescence (CL)image and characteristics of Th, U and REE. And the weighted mean age of 206Pb/238U to the western and eastern plutons are 229.6±0.8Ma (MSWD=0.44) and 232.8±1.5Ma (MSWD=0.21) respectively measured by LA ICP MS zircon U Pb dating, which are consistent in error range. Accordingly, the Muztagata pluton is formed in 231.4±0.7Ma (MSWD=1.5), representing an emplacement time of the Muztagata pluton in late Middle Triassic. Furthermore, the rocks are interpreted to have derived from magma mixing between crust and mantle by the proofs of petrology characteristics, internal structure and REE patterns of zircons, geochemistry data of predecessors. From the above and based on the regional geological data, Muztagata pluton was formed in the transitional period from primary collision to post collision, indicating that the primary collision of Paleotethys in Western Kunlun occurred before late Middle Triassic, and entered post collisional period from then on.