Achieving satisfactory organic pollutant oxidation with a low concentration of peroxymonosulfate (PMS) is vital for persulfate-involved advanced oxidation processes to reduce resource consumption and avoid excessive sulfate anion (SO42−) production. Herein, efficient conversion of dissolved oxygen (DO) over single-atomic Fe–N3O1 sites anchored on carbon nitride for efficient contaminant degradation is fulfilled, triggered by a low concentration of PMS (0.2 mm). Experimental and theoretical results reveal that the preferentially adsorbed PMS onto atomic Fe–N3O1 center can deliver electrons toward the single Fe atom to increase its electron density to trigger DO reduction into superoxide radical (O2• −) and successive transformation into singlet oxygen (1O2), which is quite different from the conventional PMS activation process mostly depending on PMS itself function for reactive oxygen species generation. On the other hand, PMS with high concentration could occupy active Fe–N3O1 sites to hamper DO conversion and further produce massive SO42−. A couple of -Fe-CN0.05 -and slight PMS is effective for actual kitchen wastewater remediation and long-term bisphenol A degradation. This work elucidates the triggering role of low-concentration PMS in DO conversion over a single-atom Fe catalyst, which can inspire the development of resource-saving, cost-effective, and environmentally-friendly catalytic oxidation systems for environmental restoration.