Baiyinnuoer Lead- Zinc deposit in Inner Mongolia is a famous superlarge skarn type lead zinc deposit in North China. The magmatic rocks exposed in the mining area mainly include granodiorite，crystalline tuff lava，quartz porphyry，diorite porphyrite and granite. The ore body is vein and saccate， occurring in the marble of the Zhesi Formation of Middle Permian age， and controlled by the silicalcium surface and NE trending fault structure. There are two different views on the metallogenic age of Baiyinnuoer Lead- Zinc deposit： the Yanshanian and the Indosinian ages. In this paper， the age of the ore body is inferred by determining the diagenetic age of the magmatic rocks closely related to the spatial location of the ore body. Through the geological survey of the tunnel， it is found that the ore body cut through the volcanic rocks of the late Jurassic Manketouebo Formation in the area and then was cut through by the diorite porphyrite. Therefore， it can be inferred that the age of the ore body lies between the ages of both kinds of magmatic rocks. Through LA- ICP- MS U- Pb dating of zircon， the age of the volcanic rocks is obtained as 149. 9±2. 5 Ma，and the age of diorite porphyrite is 140. 3±2. 6 Ma， which limits the mineralization age to 140. 3±2. 6～149. 9±2. 5 Ma，i. e. to late Jurassic- Early Cretaceous which is consistent with the formation age of tin polymetallic deposits in the region. Tin- rich minerals have been found in Baiyinnuoer Lead- Zinc deposit and tin ore bodies have been found in its surrounding areas. The formation of tin polymetallic deposit in the area is closely related to the high evolution granite in the late Jurassic Early Cretaceous. Therefore，it is proposed that the metallogenic body of Baiyinnuoer Lead- zinc Deposit may be the concealed under the high evolution granite of the same period， suggesting that there is still a huge prospecting prospect in the deeper part of the deposit.