Abstract: The purpose of this paper is to study the fatigue life prediction model of interior failure and the reliability evaluation of residual life of carburized 12CrNi3 alloy steel under variable stress levels. Through the fatigue experiment under stress ratio R=-1, based on the interior fatigue failure mechanism of the specimen, combined with the crack growth rate, the life prediction model of interior fatigue failure is established.Based on the three parameter Weibull distribution law of fatigue life under the variable stress levels, the reliability model and probability density model of residual life under prior life are constructed. The results show that: the predicted fatigue life has a high prediction accuracy within 3 times factor. Under the prior life, the reliability and probability density decrease with the increase of residual life.