By use of RNG k-ε turbulence model and VOF method tracking the free surface,the paper carried out 3D numerical simulation to hydraulic characteristic of open channel with flexible submerged plants.The submerged flexible plants area is simplified as porous medium region ,the porous medium model was selected to simulate the influence of porous medium on water flow.It is set up that porous medium model has no effect on generation and dissipation of turbulence,and the permeability rate of porous media model is determined by the pressure difference.The porosity rate is determined by flexible plant space volume ratio. The simulation results gave the curve of water level along open channel and the vertical distribution of velocity of flow and turbulence intensity.At the last,it compared the numerical simulation results with test results.Both the result are in good agreement,which means that the numerical simulation by use of porous media region instead of flexible submerged plants is feasible.