Abstract: The air cushion surge chamber has a good function for reflecting water-hammer waves. That is why it can effectively reduce water hammer pressure in the pressure pipeline when the load of hydroelectric power station change dramatically. However, the leakage is always restricting the popularization and application of the air cushion surge chamber at a large scale. To solve such problems, a new technique which can effectively prevent the leakage of pressure gas is put forward in this paper. We can place rubber bags as a kind of obturator devices in the traditional air cushion surge, as a result, the rubber bags can confine gas and the surrounding rock just undertakes structural load. The new air cushion surge chamber with add-on rubber bags can successfully realize the separation of confining gas and bearing load. The air cushion surge chamber with add-on rubber bags that has the advantages of softness, low elastic modulus, and good sealing, is first put forward to radically solve the problems of pressure gas leakage when the closed thin shell is cracking. At the same time, it can achieve the seamless merge between the rubber bags and the surrounding rock of the air cushion surge chamber. Based on the theory of fluid mechanics and water level fluctuation in the air cushion surge chamber, the constitutive relation between stress and deformation of the rubber bag is well analyzed and then the calculation formulas of air needed to be pushed into a single rubber bag or multiple ones are deduced. They can meet with the force balance principle, the stress-strain relationships of the rubber material, as well as deformable coordination condition of the surge chamber. The new method for preventing leakage provides theoretical references for design and construction of the air cushion surge chamber and for engineering control in the process of operation.