Abstract: Through the model test ,this paper investigates the hydraulic characteristics of the swirl tunnel containing a barrage, which include pressure, rotational flow angle, swirl cavity pocket diameter, and so on. After the barrage is installed, the positive pressure of the level section in the hole between the fastening device and the barrage is increased obviously, the change of pressure along length is reduced; with the action of centrifugal force, there exists twophase flow which is mixed enough by air and water behind the barrage outlet，the velocity is reduced, the cavitation probability grows downwards, and the range of the swirl tunnell is decreased; with the decrease of swirl cavity pocket diameter, the ventilating amount will be less. Except for the lowerof the discharging capacity, the barrage effect in the level rotary internal energy dissipation discharge tunnel is benefit to the project, therefore, we can make use of it to improve the structural design and preventive measure when the diversion tunnel will be rebuilt.