Abstract: The frequency and intensity of extreme weather events such as extreme rainstorm floods have been increasing significantly with the global warming. Rainstorm floods could not only have profound impacts on both human society and the natural environment, but also change the fluxes of terrestrial materials to the sea, causing the diffusion path and range of water flow and sediment, which is very significant for the evolution of estuaries. An extraordinary rainstorm event occurred in Zhengzhou, Henan on July 17-23, 2021, causing severe flooding in the lower reaches of the Yellow River. Based on measurement data and satellite remote sensing, we discussed the hydrological characteristics, stratification structure, and dynamic mechanism of the Yellow River Estuary before and after the flood and in the early and late stages. Results show that the average daily runoff at Lijin station was 1.95×10⁸ m³ and the sediment transport amounted to 1.58×10⁶ t during the flood, which is 2.71 times and 9.38 times of that in non-flood period, respectively. Since the duration of high flow and flood cycle were shorter than those during the period of the water-sediment regulation scheme (WSRS), the runoff and sediment flux into the sea during this rainstorm flood is slightly lower than that of the WSRS. Moreover, the turbidity and salinity of the Yellow River estuary changed significantly during the flood, which were associated with the enormous water and sediment discharge of the Yellow River. The turbidity increased obviously and the range of high turbidity zone became wider. In addition, diluted water expanded to the surface to the northwest and southeast directions. However, sediments were blocked by the tidal shear front near the coast, which narrowed the diffusion range of sediments significantly. Compared with artificial floods, the impact of rainstorm flood on estuarine salinity was relatively small, the plume diffusion range was relatively limited, and the sediment diffusion range was less different from that of artificial flood, which is in line with the sedimentation range of sediment entering the sea under the barrier of tidal shear front. The runoff of the flood event also caused a high degree of water stratification in the Yellow River estuary. The buoyancy frequency of the surface water mass could reach more than 10⁻¹ s⁻², which was an order of magnitude difference from the buoyancy frequency after the flood. However, the buoyancy frequency of the middle and bottom water column change less during and after the flood, which is mixes well than the surface water column.