<p>Addressing the challenge of controlling transient oxygen concentration in gas-sensitive photoreactions, this paper reports a microflow process based on a “dual oxygen supply” strategy, successfully applied to the photocatalytic oxidative synthesis of 2-phenylbenzothiazole. This strategy integrated oxygen pre-dissolved in the solvent with oxygen permeating through the microreactor wall, maintaining the dissolved oxygen concentration in the reaction system within a controllable low range, thereby effectively avoiding the severe promotion of oxidation side reaction observed in conventional gas-liquid slug flow where direct gas-liquid contact driven dissolved oxygen close to saturation throughout the reaction. The results revealed the differentiated sensitivity of the main and oxidation side reaction to oxygen concentration: the oxidation side reaction exhibited significantly higher sensitivity than the main reaction. Based on this mechanistic insight, three oxygen supply modes and microflow operation protocols were developed for low (4 mmol/L), medium (20–40 mmol/L), and high (100 mmol/L) initial substrate concentrations, respectively. At a low concentration, relying solely on atmospheric oxygen (O₂ at 0.1&#xa0;MPa absolute pressure) permeation and solvent pre-dissolved oxygen, complete conversion was achieved within 8&#xa0;min with a yield of 77%. At a medium concentration of 20 mmol/L, initial dissolved oxygen saturation and external positive-pressure permeation afforded a 70% yield within 40&#xa0;min. At a high concentration, an “on-demand oxygenation” cyclic microflow process was developed, delivering a yield of 74% while maintaining a selectivity of 75%, with a space-time yield enhanced by 7-fold and a total productivity enhanced by 4-fold compared to the batch process. This study offers a practical and flexible microflow technology pathway for the efficient implementation of gas-sensitive photoreactions.</p> Graphical Abstract <p></p>