Channel system consisting of tidal river system is affected each other. The water flows are affected comprehensively by upstream inflow, tide in outflow and hydraulic structure. The hydrological regime is very complicated. The hydrological prediction method and numerical simulation method is united to simulate water flows in river system with the design flood hydrograph as the upstream boundary condition and the tide induced from downstream boundary and gate control. Many cases of combination of design flood and tide are simulated, which are used for regulating the river system.