<p>When a diesel engine is frequently started and stopped, the piston is susceptible to thermal fatigue failure due to cyclic thermal shock loads. Evaluating the piston’s thermal fatigue life is a crucial aspect of assessing diesel engine reliability. Traditional experimental methods are time-consuming and costly, placing a significant burden on enterprises. This article proposes a thermomechanical fatigue analysis method to evaluate the thermal fatigue life of pistons, based on the theories of thermoelastic plasticity and thermal fatigue damage. Thermal fatigue tests and numerical simulations were conducted on aluminum alloy pistons to validate the effectiveness of the method. The influence of loading sequence on the life of aluminum alloy pistons was investigated, and the thermal fatigue mechanism of these pistons was elucidated. The results show that the thermal fatigue life of aluminum alloy pistons predicted by the thermomechanical fatigue analysis differs from the experimentally measured life by only 2.7%, indicating that this analysis method can reliably evaluate piston thermal fatigue life. The loading sequence significantly impacts the thermal fatigue life of the piston; compared to a low-to-high loading sequence, a high-to-low loading sequence results in a shorter thermal fatigue life. Under cyclic thermal loading, cyclic stress occurs at the interface between aluminum and silicon within the piston, where microcracks initiate at stress concentration sites. These microcracks subsequently propagate and coalesce, eventually developing into macroscopic cracks.</p>