The causes of the Yellow river flow-stopping can be at tributed to the characteristics of lake and marsh as main landforms, rare precipi tation, disparity in annual runoff amount between dry and moist year, water resources shortage, lake surface evaporation, the cold climate in winter, and the periodic variation of annual runoff amount in the source area. Among which, shortages of water resource and lake surface evaporation are the major reasons. The flow-stopping showed periodicity analysing from the hydro-data. It was the results of natural factors,so the flow-stopping now should not be considered as emblem of eco-envi ronment worsening.