[Objective] The operation of cascade reservoirs in the lower reaches of Jinsha River has significantly altered the inflow flood characteristics of the Three Gorges Reservoir (TGR), posing new requirements for the adaptability of existing flood control scheduling. This study aims to reveal changes in inflow flood processes and flood propagation characteristics within the TGR after the impoundment of cascade reservoirs in the lower reaches of Jinsha River, providing a theoretical basis and data support for scientific flood control scheduling of the reservoir. [Methods] Based on the measured hydrological and topographic data of the TGR from 2003 to 2020, mathematical statistical methods were employed to analyze changes in inflow flood characteristics before and after the impoundment of cascade reservoirs. A one-dimensional hydrodynamic model was adopted. After calibration and validation, multiple comparative scenarios were designed to conduct simulation and analysis of flood peak propagation processes in the TGR area. [Results] Statistical analysis of the measured data showed that around 2013, the average inflow flood volume of the TGR decreased by approximately 9.9%, while the rising and falling durations decreased by 4.9% and 9.9%, respectively, and the average rising and falling rates increased by 10.3% and 9.8%, respectively. These results indicated that the flood recession became faster, the flood peaks occurred earlier, the average peak discharge decreased, and the risk of extreme floods increased. The mathematical model results showed that, in terms of discharge characteristics, the flood peak propagation time was positively correlated with the flood peak discharge, while the influence of changes in baseflow was not significant. In terms of hydrograph shape, the flood peak propagation time was negatively correlated with the rising duration and positively correlated with the falling duration. In terms of boundary conditions, the flood peak propagation time was negatively correlated with the water level upstream of the dam. [Conclusion] The operation of cascade reservoirs significantly reduces inflow flood peak, and the attenuation effect on the flood hydrograph also leads to a significant increase in flood duration. The flood peak propagation is faster under conditions of lower peak discharge, longer rising duration, shorter falling duration, and higher water level upstream of the dam.