Abstract: An analysis was conducted on the uncertainty factors affecting the tensile strength of EPDM rubber after hot air aging, and a mathematical model of uncertainty was established. The effects of repeated testing, maximum force recorded during sample stretching, thickness, width, and fluctuations in hot air aging temperature on uncertainty were analyzed. The results show that the factor of repeatability testing had the greatest impact on uncertainty, while equipment such as microcomputer controlled electronic universal testing machines, thickness gauges, reading microscopes, and hot air aging chambers had a relatively small impact on uncertainty.