Single-atom　transition　metal-nitrogen-doped　carbons　(SA　M-N-Cs)　catalysts　are　promising　alternatives　to　platinum-based　catalysts　for　the　oxygen　reduction　reaction　(ORR)　in　proton　exchange　membrane　fuel　cells　(PEMFCs).　However,　enhancing　their　performance　for　practical　applications　remains　a　significant　challenge.　This　review　summarizes　recent　advances　in　enhancing　the　intrinsic　activity　of　SA　M-N-C　catalysts　through　various　strategies,　such　as　tuning　the　coordination　environment　and　local　structure　of　central　metal　atoms,　heteroatom　doping,　and　the　creation　of　dual-/multi　metal　sites.　Additionally,　it　discusses　methods　to　increase　the　density　of　M-Nx　active　sites,　including　chelation,　defect　capture,　cascade　anchoring,　spatial　confinement,　porous　structure　design,　and　secondary　doping.　Finally,　it　outlines　future　directions　for　developing　highly　active　and　stable　SA　M-N-C　catalysts,　providing　a　comprehensive　framework　for　the　design　of　advanced　catalysts.