The invention provides a sealing capacity test device for liquid medium sealing rings, including a cylinder body which has a cavity, a test piston which is sleeved with a sealing ring under test and seals a first end of the cavity, an adjusting piston which seals a second end of the cavity, an adjusting part which presses against the adjusting piston to push the adjusting piston to move in the cavity, and a measuring part which is used for measuring the pressure in the cavity. In the invention, the pressure of an oil medium can be adjusted automatically by changing the stroke of the adjustingpart, additional equipment providing a high-pressure oil source is not needed, and the test implementation process becomes simple and easy. By replacing the test piston sleeved with the sealing ring under test, the sealing effects of different static sealing products can be tested, and the cost can be reduced. Moreover, the device can directly cooperate with an environmental test box to simulate the change of sealing ability of a sealing ring in different temperature environments.