Based on the flow characteristics of an actual water-blocking hydraulic structure, the internal boundary method, the equivalent discharge roughness correction method, and the equivalent discharge topographic correction method were used to correct the discharge capacity, in order to fit the simulated discharge capacity with the actual discharge. Simulation of water level and flow velocity was conducted under the conditions of steady flow and unsteady flow in a two-dimensional hydrodynamic numerical flume model to compare the three methods. The results show that the former two methods can accurately reflect the discharge and the properties of the flow around the water-blocking hydraulic structure, and the water level and flow velocity simulated by the third method, due to the local topographic change, excessively deviated from the actual values.