Compared with previous years，the duration of high water-level and large flow was longer in 2020. At the same time，the channel became shallower due to sediment deposition in flood season，which causes unsafe factors for the normal operation of the channel. On this basis，we analyze the impact of catastrophic flood and the possible causes and countermeasures of channel deterioration. The results show that sediment deposits in the riverbed during the flood season is scoured during the dry season，and channel conditions depend on flood season deposition versus post-flood scouring. The long duration of the 2020 flood and the relative lack of time to recede after the flood results in the inadequate scour and navigation-obstruction in the upper shallow area，therefore emergency dredging is required to maintain the waterway conditions. We suggest to pay more attention to the channel changes and water conditions in this region in the next few years to formulate corresponding channel maintenance measures in time.