Abstract: Since the 1980s, the flow-sediment regime entering the Lower Yellow River (LYR) has altered significantly. The channel in the LYR continuously experienced aggradation under the heavy sediment load and degradation by the operation of the Xiaolangdi (XLD) Reservoir. Based on the measured flow-sediment data and the topography at fixed sections from 1986 to 2020, the reach-scale bankfull discharges were calculated, and the contributions were quantified of flow-sediment regime during the flood and non-flood seasons to the flood discharge capacities in different reaches. Results show that: ① In the pre-dam period, the fluvial erosion intensity decreased temporally, leading to a predominance of channel aggradation with deposition in flood seasons and erosion in non-flood seasons. Consequently, the bankfull discharge decreased continuously with the minimum value less than 2 000 m³/s. ② In the post-dam period, the fluvial erosion intensity increased significantly especially in the non-flood seasons, contributing greatly to the channel degradation. The flood discharge capacity recovered remarkably, with the most rapid recovery occurring in the braided reach. ③ There was a close power law relationship between the bankfull discharge and the 5-year average fluvial erosion intensity during the flood and non-flood seasons, reflecting the cumulative impact of flow-sediment regimes in the flood and non-flood seasons on the flood discharge capacity. ④ Owning to the upstream damming, the contribution of the flow-sediment regime in non-flood seasons to the flood discharge capacity increased especially in the braided reach (53%), while it was lower in the transitional and the meandering reaches (less than 20%).