Accelerated degradation testing has been widely used to investigate the reliability of long lifetime products, including rubber seals. The test results at higher stress levels were extrapolated to the normal stress level in the accelerated degradation testing. For an accurate product reliability evaluation, the failure mechanism under accelerated stresses should be consistent with the mechanism under normal conditions. Based on the likelihood ratio test, an identification method and a flow chart were proposed. For describing the mechanism consistency and variation, log-linear and non-log-linear acceleration models were suggested, and the mixed-effects model was introduced to depict the degradation process. According to the judgment between the consistency and variation of acceleration model parameters, the identification was completed. The simulation test and the real test show that this method can identify the mechanism variation of rubber seals. Moreover, the stress boundary for consistent mechanism is found by the identification method.