In this study, we focused on methional, a characteristic flavor compound of Sesame aroma baijiu, and investigated its production during the stacking fermentation of baijiu jiupei. It has been speculated that the Maillard reaction occurs during the stacking fermentation, which results in the production of methional. This research showed that methional increased during the stacking process, reaching 0.45mg/kg in the later stage of stacking fermentation. To simulate the stacking fermentation, a Maillard reaction model was established for the first time with conditions determined based on the measured stacking parameters (pH, temperature, moisture, reducing sugars, etc.). Through the analysis of the reaction products, we found that it is highly possible that the Maillard reaction occurs during the stacking fermentation, and a potential formation route of methional during the process was elucidated. These findings provide insights for the study of relevant volatile compounds in baijiu.