The invention discloses a test method for CO2 resistance of a rubber sealing ring, and the method is used to test the high-pressure CO2 sealing capability of a rubber O-shaped ring for an electronic pressure gauge in the well testing field of a CO2-driven oil reservoir. A rubber O-shaped ring clamp and a pressure vessel simulate the practical single-side bearing state of the sealing ring for the electronic pressure gauge, a temperature-constant air experimental case, a CO2 gas-liquid booster pump and the like are used to simulate extreme working environment conditions including temperature, pressure and medium of the sealing ring, the leakage pressure of the rubber O-shaped ring is measured after simulated test processes that the electronic pressure gauge is placed into a well, deepened gradually, fluctuates with pressure and placed out of the well, and the high-pressure CO2 resistant sealing performance of the rubber O-shaped ring is determined according to the leakage condition and the physical appearance of the rubber-ring after test.