Abstract: Changchengian Period Gudongjing Complex-Group serves as the first sedimentary cover on the ancient folded base-ment in Beishan region of Inner Mongolia, but without reliable dating data. Previous researchers assigned it to Mesoproterozoic Changchengian Period only on the basis of the contrast with the Changchengian system of the Yanshan area in such aspects as for-mation layers and rock association characteristics. In this paper, the LA-ICP-MS zircon U-Pb method was used for the determi-nation of the age of the detrital zircon in metamorphic quartz sandstone of the Gudongjing Complex-Group, and the test results show that the 90% ages of zircon ²⁰⁷Pb/²⁰⁶Pb data are 1.3~2.2Ga, the rest of ages are 2.4~3.2Ga, peak period ages are 1.6~2.0Ga, and the youngest ²⁰⁷Pb/²⁰⁶Pb age of detrital zircon is 1393±50Ma. Based on comparing the age spectrum of the detrital zircon with the formation age of the surrounding massif, the dertital zircon limits the sedimentary age of the Gudongjing Complex-Group as the Mesoproterozoic Jixianian Period. The sediments of the Gudongjing Complex-Group might have come from Beishan-Alxa and Tarim-Dunhuang blocks.