Abstract: Kemuqi gold-placer area is an important part of Xishan region where has been famous for producting placer-gold for a long time. A primary study on grain-size and sedimental environment of the placer shows that the deposits with rich placer golds are usually characterized by a higher percentage of silt and clay and poorly-sorting. According to the analysis, the authors believe that the deposits belong to a kind of fluvial sediment. It is different from the overlying sediment. The cause of formation of the placer is a long and complex precess. The placer-gold was mainly produced in the period when the flow had a very strong energy to transport the debris. So the flow power play an important role in transporting and depositing placer-golds in Altai Mountains.