In the plain river network area, the mobility of rivers is usually poor and the ecological flow velocity of rivers is difficult to be guaranteed. Taking Haishu District of Ningbo City, a typical plain river network area, as an example, a field prototype synchronous monitoring experiment was carried out. The effect of water diversion on hydrodynamic regulation was systematically studied with the river diversion ratio, water exchange rate and storage capacity as the research objects. The results showed that:The hydrodynamic improvement effect of plain river network was closely related to the position of water inlets and outlets and water diversion flow. To ensure a good water exchange rate, the connection of water inlets and outlets should run through the whole area as far as possible. The water exchange rate of plain river network area had strong heterogeneity in spatial distribution (under the four schemes, the maximum range of water exchange rate was 190% and the minimum was 75%). The water diversion project could improve the hydrodynamic characteristics of the branches with large diversion capacity, but it was not helpful for the branches with small diversion capacity and truncated creek. The improvement of regional hydrodynamic needed to increase the water exchange rate and decrease the change rate of storage capacity, the smaller change rate of storage capacity in Haishu district was about 0.2%. The study analyzed the water conveyance capacity and water exchange rate, which has reference value for optimizing the generalized density of river network to reduce the simulation deviation and provides a basis for exploring the improvement of water dynamics in plain river network and promoting the water environment quality. It will also be conducive to river regulation with special hydrodynamic characteristics and regional water environment control.