An online degradation model is presented, in which is avoided the error in parameter degradation accelerated test, which is caused by temperature shock during parameter measurement. Through the measurement with avoiding the error parameter, the parameter degradation model can be more accurate. To demonstrate the application of the method, a kind of mature product, 3CG120, is tested in a temperature range of 150230 ℃ under online process-stress. Then the error of lifetime is obtained by utilizing the online model to be about 6.5%, much less than that of the old model (23.2%).