According to the demand of large-scale simulation, a numerical simulation model for vegetated flows was developed based on two-dimensional unsteady flow equations. According to the experimental flume results, the influence of aquatic plants on water flow was investigated. The vertical distribution characteristics of the drag coefficient induced by flexible vegetation at different positions of vegetation patches were obtained. The drag coefficients obtained from the experiments were substituted into the model to verify the model’s reliability and explore the flow characteristics of open channels with vegetation patches. The results show that: 1) the simulation results of the model are in good agreement with the measured data, which can well simulate the water flow process under the influence of vegetation patches, especially for the far areas with weak three-dimensional effect; 2) The water-blocking effect of the vegetation patch reduces the flow velocity inside the patch and increases the flow velocity in the non-vegetated area on the side, forming a longitudinal shear effect at the edge. The proposed model can support the dynamic analysis of vegetation in rivers, lakes, and estuarine wetland systems.