The Yellow River is the 2nd longest river in China and the 6th longest river in the world. However, the timing and mechanism of its integration remains debated. During the establishment of its present geometry, the Yellow River captured and deeply incised into a series of local drainage basins along its Upper and Middle Reaches. The termination of basin filling, therefore, can be linked to the development of the Yellow River. The Sanmen paleolake, a Plio-Pleistocene endorheic mega-lake situated in the Fenwei Basin, was the last catchment basin captured by the Yellow River before it emptied into the sea. The final termination of the lacustrine deposition in the Fenwei Basin can therefore indicate the integration of the Yellow River. Here, we present the results of a detailed magnetostratigraphic and magnetic susceptibility study of a lacustrine-loess section from the southeastern part of the Fenwei Basin (Sanmenxia Subbasin), and aim to (1) explore the sedimentary evolution of the Sanmen paleolake and refine the age of the Sanmen Formation in this area, and (2) investigate the precise timing of the integration of the Yellow River. Our results show that the Sanmenxia Subbasin was occupied by a salty lake between 2.7 and 2.2 Ma, then it gradually changed to an alternation of shallow lake and floodplain environments between 2.2 and 1.6 Ma, and it finally irreversible dried up at ~1.6 Ma and was subsequently covered by loess-paleosol sequences. The drying up of the Sanmen paleolake at ~1.6 Ma indicated the establishment of the connection between the Middle and Lower Reaches of the Yellow River.