Abstract: Controlling the outlet flow rate at the lower boundary of a river can alter the flow rate and direction of the water body,leading to an improvement in the water quality of the river,the improvement effect is related to the scale of diversion and drainage,the layout of the outlet,etc.Scientific and rational allocation of water resources is the core of sustainable water resources use.This paper presents a case study of the river network area of Jiangbei Zhenhai Plains,Ningbo,for example,and selects the simulation period from October 1 to November 1,2022,NH₃-N as an indicator for the main pollutant,construction of a one dimensional non-constant flow dynamics MIKE11 water quality and water quantity coupling model,taking into account the outflow capacity of the outflow pump station and maintains the minimum water consumption in the basin.The study sets up 28 outflow scenarios with outflow flow rates of 9,18,24 and 36 m~3/s through the combination of three outflow opening and closing arrangements.This study aims to simulate the impact of boundary outlet flows on water velocity in various scenarios using a coupled water quality and water quantity model,and analysis of water quality change characteristics.The results show that:（1）The higher the outlet flow of the basin,the more significant the increase in the flow velocity of the watershed,comprehensive hydrodynamic and water quality factors,the outflow of 18m~3/s can better improve the hydrodynamic conditions and water quality of the river.However,if the flow rate increases to 24 or 36 m~3/s and only one or two outlets are opened,the river has the risk of overflow.Therefore,opening more outlets is recommended to ensure flood safety;（2） the optimal solution after simulation makes the average flow rate of the basin reach 0.056 m/s,the average concentration of NH₃-N decreases to 1.660 mg/L,the water quality improvement rate reaches 17.0%,the water quality condition of the river can be improved from poor V to IV or V water standard,the results provide a reference basis for improving the hydrodynamic water quality of the river.