Abstract: Xaitongmoin County belongs regionally to southern subbelt of Gandise granite belt and possesses extremely developed intrusive rocks. In geological map, there are Cretaceous, Paleogene and Neogene rock masses. Through isotopic chronologic study, the authors obtained 12 zircon U-Pb age data and, on such a basis, separated a Jurassic intrusive body from the previously-assigned Cretaceous, Paleogene and Neogene rock masses. According to its rock type, this Jurassic intrusive body is incorporated into the Early Jurassic Dorecun series and Middle Jurassic Donggaxiang series. Zircon U-Pb isotopic age of Yuelagamo rock body within the Jurassic intrusive body is 166.9±2.8Ma, suggesting Middle Jurassic Barou period.