Abstract: As an important infrastructure for river protection and efficient utilization of water depth resources,river and channel regulation works have always been the focus of attention on the effect of their operation on the distributary relationship of branches,the shape of shoals and channels,and the improvement of deep-water resource.In this study,that Zhenyang reach of the low Yangtze River is taken as the research object,and through the analysis of the field data from 1959 to 2021,the regulation mechanism of the distributary relationship of the branch and the shape of the beach and trough under the joint action of water and sediment conditions and waterway engineering are studied.①From 1981 to 2021,the Zhenyang reach is in a cumulative erosion situation,and the characteristics of riverbed erosion and deposition before and after the operation of the Three Gorges Project are “deep channel erosion and beach deposition”;②The left branches of Shiyezhou and Hechangzhou are flood-prone branches,the left branch scouring development has been caused from 1972 to 2015,and the diversion ratio has increased.After the implementation of the second phase project,the diversion ratio has decreased by 6.1%~6.4% and 8.3%~8.8% respectively (flow rate 20 000~30 000m³/s,2016~2021),which means that the channel project has effectively regulated the diversion relationship of branches;③After the implementation of the second phase project,the integrity of the beach Shiyezhou is enhanced,and the channel volume of the right branch increases by 0.0554×10⁸m³ when the diversion ratio of the right branch of Shiyezhou increases by 1.0%,but the increasing rate of the channel volume of the left branch is still higher than that of the right branch.Therefore,it is suggested that the engineering measures of limiting the flow in the left branch and improving the integrity of the beach boundary should be taken in the subsequent improvement project.④After the implementation of the second phase project,the channel volume of the right branch will increase by 0.0158×10⁸m³ when the diversion ratio of the right branch of Hechangzhou increases by 1.0%.However,the shrinkage of the Zhengrunzhou point bar and the development of channeling are not conducive to the stability of the diversion relationship.In the follow-up improvement project,it is suggested to take engineering measures to moderately reduce the diversion ratio of the left branch or widen the entrance of the right branch to realize the drainage of the main navigation channel.