Understanding the deactivation behavior of photocatalysts during volatile organic compounds (VOCs) degradation is crucial for their practical application. In this study, the photocatalytic deactivation mechanism of Bi2O2CO3 during toluene degradation was investigated under continuous-flow conditions. A time-dependent decline in photocatalytic activity was observed, which was attributed to the accumulation of stable intermediates on the photocatalyst surface. In-situ DRIFTS revealed a sequential transformation of toluene into benzyl alcohol, benzaldehyde, and benzoic acid, followed by the formation of ring-opening products. However, the incomplete mineralization of benzene ring-containing intermediates resulted in their gradual accumulation, causing catalyst deactivation. These finding elucidates the mechanism governing the deactivation of Bi2O2CO3 photocatalysts and highlight the necessity of developing strategies to enhance intermediate mineralization for long-term photocatalytic activity.