Abstract: A standard κ-ε model， a RNG κ-ε model， a Realizable κ-ε model and a standard κ-ε model combined with VOF method which can get the free surface of water are applied to simulate the vortex flow in the flood discharging tunnel of Gongboxia Hydropower Station respectively.The validity of the calculation is verified by the prototype data， and the RNGκ-ε model is more applicable than others. Then the vortex-type tunnel and its posterior segment are simplified to a straight tunnel and the barrage is placed in different locations. The RNGκ-ε model is applied to simulate the internal flow. By comparing and analyzing the rate of energy dissipation， pressure distribution and cavitation number， the optimum location for placing the barrage and the corresponding turbulent characteristics are obtained by numerical simulation. It can be found from the change tendency of the turbulence kinetic energy and the dissipation rate that there is a same change rule between the both sides mentioned above, and this fully shows that the greater the turbulency kinetic energy is, the higher the dissipation rate is.