High-performance electrocatalysts are required because the sluggish kinetics of Oxygen Reduction Reaction (ORR) at the cathode in either Fuel Cell (FC) or Metal-Air Battery (MAB). The current most effective ORR catalysts are noble Pt-group metals, whose high price and low abundance severely hamper the widespread application of FC and MAB. Dispersively non-noble transition metal coordinated with nitrogen atoms doped in carbon nanomaterials (M-N-C) Single Atom Catalysts (SACs) have been considered as the most promising catalysts for the ORR. Here, the effect of typical morphology on the activity and stability of SACs was discussed firstly. Moreover, the effect of metal type, coordination nitrogen number, heteroatom decoration on the central metal atom were discussed. Based on the rate determining step (RDS), we propose the ideal characters that high-performance SACs should possess.