Abstract: Abstract：The authors analyzed early Pleistocene lacustrine strata at Zhagenjialong (1919.6 ka B．P．), in borehole K5 (1135.9 945.4 ka B．P．) and on the west bank of the Yeniu River (1548.2－765.4 ka B．P．) and fossil plants and sporopollen data in various section in early Pleistocene lacustrine strata at Zhagenjialong. The analytic results show that in the early part of the early Pleistocene there occurred a subtropical hilly coniferous forest vegetation landscape in the source area of the Yellow River, and that in the strata woody plants predominate, mainly including needle leaf plants such as Picea, Pinus, Abies and Tsuga, indicating a flourishing period of animal and plant growth in the source area. At the beginning of the late Early Pleistocene, pollen of arborous plants was rapidly reduced and even all disappeared, and pollen of herbaceous plants increased significantly. At the end of the late part, sporopollen was diluted, with pollen of herbaceous plants predominating, showing a landscape of desert steppe vegetation. The formation of the present eco-geological environment in the source area of the Yellow River is the inevitable result of geological evolution.