Abstract: With increasing environmental regulations and the promotion of resource recycling, desulfurized fly ash, a byproduct of coal-fired power generation, has potential applications in enhancing the performance of autoclaved aerated concrete （AAC）. To deeply investigate the impact of desulfurized fly ash dosage on the stability of AAC and its mechanisms, stability experiments are conducted using various proportions of desulfurized fly ash to replace ordinary fly ash. The consistency and dry density of six different mix proportions are tested, and the influence on the compressive strength of AAC specimens is analyzed. Alongside the hydration process of AAC, the effects of desulfurized fly ash from the micro to macro levels on the structure and performance of AAC are explored, elucidating the mechanisms by which desulfurized fly ash affects the stability of autoclaved aerated concrete. The study shows that in the initial phase of incorporating desulfurized fly ash, due to its role as a micro-filler and its enhancement of the hydration reaction, there is a significant improvement in the dry density and early compressive strength of AAC, with the strength of AAC specimens reaching a threshold at 30% fly ash content. However, the addition of desulfurized fly ash has a bidirectional effect on AAC. Excessive amounts lead to an increase in porosity and a decrease in reactivity, subsequently affecting the long-term stability of the specimens. These findings provide significant references for optimizing AAC processes, offering a theoretical basis and data support for the application of desulfurized fly ash in the field of autoclaved aerated concrete.