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Since this century, due to the dual influence of climate change and strong human activities, the water and sediment conditions en- tering the Lower Yellow River (LYR) have changed significantly. Consequently, the cross-sectional geometry of the LYR channel has been adjusted drastically under the long-term non-equilibrium sediment transport state, which affects river regime stability directly and threatens the flood control safety on both sides of the river seriously. In this paper, based on the measured cross-sectional data of Baihezhen-Gaocun reach of the LYR from 2001 to 2021, the evolution characteristics of the morphological parameters of cross-section were analyzed. On this basis, Heigangkou-Liuyuankou reach was selected as the proto type and a physical model experiment was conducted, to quantitatively reveal the adjustment of cross-sectional morphology under non-equilibrium sediment transport conditions. The analysis of the prototype measurement data found that cross-sectional morphology of the Huayuankou-Jiahetan reach was more variable compared with other sections of the LYR. A typical river section in the Huayuankou-Jiahetan reach was selected as the prototype, and a physical model was constructed using a horizontal scale of 600 and a vertical scale of 60. Keeping the same initial river boundary conditions, channel morphology adjustment experiments with four types discharges of 2 000 m³/s, 3000 m³/s, 4000 m³/s and 5 000 m³/s and different inlet sediment concentration were carried out. The experiment results show that when the inlet sediment concentration is small, the main channel erosion, the area increases and the river phase coefficient decreases. When the inlet sediment concentration is large, the main channel sedimentation, the area decreases and the river phase coefficient increases. Comparing the experimental data with the prototype data, the analysis reveals that the morphological parameters at river reach scale are well correlated with the incoming sediment coefficient under non-equilibrium sediment transport conditions, among which the main channel area is exponentially negatively correlated with the incoming sand coefficient, and the river phase coefficient is qua- dratically correlated with the incoming sediment coefficient. [ABSTRACT FROM AUTHOR]