Replacement of enzymes with nanomaterials such as atomically dispersed metal catalysts is one of the most crucial steps in addressing the challenges in biocatalysis. Despite the breakthroughs of single-atom catalysts in enzyme-mimicking, a fundamental investigation on the development of an instructional strategy is still required for mimicking biatomic/multiatomic active sites in natural enzymes and constructing synergistically enhanced metal atom active sites. Herein, Fe₂NC catalysts with atomically dispersed Fe-Fe dual-sites supported by the metal-organic frameworks-derived nitrogen-doped carbon are employed as biomimetic catalysts to perform proof-of-concept investigation. The effect of Fe atom number toward typical oxidase (cytochrome C oxidase, NADH oxidase, and ascorbic acid oxidase) and peroxidase (NADH peroxidase and ascorbic acid peroxidase) activities is systematically evaluated by experimental and theoretical investigations. A peroxo-like O₂ adsorption in Fe₂NC nanozymes could accelerate the O–O activation and thus achieve the enhanced enzyme-like activities. This work achieves the vivid simulation of the enzyme active sites and provides the theoretical basis for the design of high-performance nanozymes. As a concept application, a colorimetric biosensor for the detection of S^2– in tap water is established based on the inhibition of enzyme-like activity of Fe₂NC nanozymes.