In order to investigate the degree of damage of rubber sealing rings under the acid fracturing condition, an experiment was carried out using HNBR O-ring in a High-Temperature High-Pressure strong acidic medium in an autoclave. The performance indicators included the rate of change of cross-sectional area, tensile properties, hardness, permanent deformation after compression, change in macro morphology and sealing properties. The experiment results showed that with the increase of cross-sectional area of the HNBR O-ring, its physical properties degenerated, and deformation, swelling and surface damage were detected after the corrosion test. The degree of corrosion damage of the O-ring in free state was more severe than that under pressurized conditions. The results showed that the HNBR O-ring has certain sealing performance within the test period, but there is a risk of sealing failure in long-term service. The study results can be used as a basis and reference for the selection of HNBR sealing ring in acidic fracturing service condition.