Abstract: Taking the hydrogenated nitrile rubber O-ring as the research object, through the simulation of the working conditions of the rubber seal, corrosion tests on O-rings were conducted at pressure 25 MPa, temperature 120 ℃, test period 168 h, and gas phase composition 5 vol%CO₂, 95 vol%N₂. Through comparing the material structure, composition, mechanical properties and fracture morphology of O-rings before and after corrosion, the corrosion damage behavior of rubber seal in high temperature and high pressure high CO₂ environment was studied. The result shows that after corrosion, the mechanical properties of O-rings decreased, and the corrosion degree in the compressive state was weaker than that in the free state, therefore, the analysis results in the compressive state should be the leading reference in a practical application. The molecular structure and fillers were damaged after corrosion, causing the performance of the rubber material decreased. The tensile fracture of the initial rubber O-ring mostly was ductile fracture, while after corrosion, it mostly was brittle fracture.