The full open discharge scouring during flood season is important for the scouring of Sanmenxia reservoir, and often presents a scouring-equilibrium process. But the current related research is still insufficient. Using the combination methods of field data analysis, theory research, experiment study and model simulation, the sediment transport law and scouring-equilibrium process of full open discharge are studied. Data analysis show that the sediment transport rate of full open discharge during flood season can be calculated by the power law relationship model by addition of the upstream sediment supply function, in which the sediment transport coefficient decrease with the increase of accumulated scouring time and volume. The decrease of sediment transport coefficient is a fundamental reason for the formation of the scouring-equilibrium process, and is an important reason for the unreasonable phenomenon of the power law index of discharge being less than 1.0 in previous calibrations. Furthermore, considering the difference of incipient motion condition for upper layer new deposited sediment and lower layer consolidated sediment, the power law relationship model is improved and the sediment transport coefficient is revised. It shows that the variation of revised sediment transport coefficient becomes more smooth and reasonable. Scouring experiment for the consolidated sediment proves that if the dry density of consolidated sediment increases slightly, the incipient motion condition (velocity, shear stress and discharge) will increase significantly. Finally, according to the principle of self-adjustment of alluvial river and using the delayed response model theory, the delayed response model for sediment transport coefficient and accumulated scouring volume are established and applied to simulate the scouring-equilibrium process of full open discharge for Sanmenxia reservoir. The simulation results show that the calculated curve of sediment transport coefficient varied with the accumulated scouring time are in agreement with the measured values, the calculated curve of accumulated scouring volume varied with the accumulated incoming water are in good agreement with the measured values. The values of determination coefficient and Nash-Sutcliffe efficiency are 0.98 and 0.98, which preliminarily illustrate the rationality of the proposed model.