The theory and method of the accelerated lifetime test is discussed, and the failure mechanism of the IGBT module is analyzed in detail. The more integrative test data is obtained by expanding the temperature range of the accelerated lifetime test. On the basis of considering the current i and the maximal junction temperatureT jmax , an improved lifetime prediction model is obtained through fitting the data of the test. The improved model is more accurate than the existent ones by the analysis and contrast of the test data errors.