One of the effect measures of improving water flow fluidity and solving city water pollution is water diversion from outside of an urban area. Because of the different boundary condition, quantity of flow distribution and velocity is different for every river. The velocity of some river channels is even much smaller. In order to enhance the fluidity of those weak rivers with small velocity, to set up a series of sluice gates and to control gates by closing and opening in some need. Thus water quantity is redistributed and the velocity is increased. For the need of investigating the effect of setting up and closing the gates, 2D unsteady river networks flow finite element model is established and verified. Bases on the model, the velocity size and orientation of the every river and water levels are calculated at the condition of whether setting up gates. These numerical researches show that the water flow quantity and velocity of flow distribution are both increased significantly for the near of river. The maximum velocity increment 0.23 m/s, the maximum banked up water level is 0.014 m, the maximum water lowering is 0.05 m, this engineering effect is obvious and this provided quantity data for the projects plan and design.