Development of high-density single atoms site (SAs) electrocatalysts is highly desirable due to their extraordinary catalytic performance. However, their synthesis is still challenging and their anticorrosion capacities in electrolyte (particularly in acidic electrolyte) are unsatisfying. Herein, we have constructed N,S co-doped carbon to anchor ~ 10 wt.% Co SAs (Co-SAs/NSC) via a novel polymerization–sulfurization–pyrolysis strategy toward selective electro-oxidation of thioethers in acidic solution. The as-obtained Co SAs has a coordination geometry of Co-S₂N₄, exhibiting excellent electrocatalytic activity and robust stability. At a low potential of 1.40 V vs. reversible hydrogen electrode (RHE), the conversion rate of thioethers over Co-SAs/NSC reaches 99.7% with 100% selectivity and 100% Faraday efficiency (FE) for producing sulfoxide, which is higher than the commercial Pt electrode and the reported state-of-the-art catalysts. Theoretical calculations and experiments reveal that the Co-S₂N₄ structure endows the outstanding electro-oxidation activity of Co SAs through significantly promoting desorption of the products. This work presents a convenient strategy to build high-performance SAs catalysts for the resourceful use of sulfur-containing pollutants.