Abstract: The development of the Yellow River was one of the major events of Late Cenozoic tectonogeomorphologic and environmental evolution in East Asia.Only by passing through the Sanmen Gorge between Shanxi and Henan and flowing into the sea,was the main stream of the Yellow River formed eventually.Therefore,the Sanmen Gorge is one of the crucial sites for the study and discussion of the formation and evolution of the Yellow River.On the basis of the important events of environmental sudden change revealed by the extinction of the Sanmen paleolake and abrupt change in sedimentation rate of the late Pleistocene loess at Mangshan,it is inferred that the Yellow River passed through the Sanmen Gorge and flowed into the sea about 150 kaB.P.,and then the modern Yellow River drainage system formed eventually.