The Tongchanggou Mo-polymetallic deposit lies in the western margin depression belt of the Yangtze landmass and is adjacent to Yidun island arc and Garze-Litang suture zone. The ore deposit is a large-size or even a superlarge deposit. Re-Os isotopic dating technique was applied, and six molybdenite samples were analyzed for Re-Os isotopic compositions, and the model ages obtained are from(82.34±1.28) to(88.27±1.23) Ma, with the isochron age being(85±10) Ma. The result suggests that Mo mineralization occurred in Yanshanian period, during which Zhongza block and Yangtze landmass collided intensively and gradually turned into post-collision stage.