Metal-superoxide is a pivotal intermediate in the oxygen activation cycle. In the biology system, heme and non-heme enzymes can activate dioxygen to generate metal-superoxide performing the C-H activation. Recently, chemists could use spectroscopic methods to investigate the metal-superoxo intermediates in the enzymes. In contrast to enzymes, which possess complicated structure not conducive for chemists to carry out related reactivity studies, using synthetic mimics for the studies of the active cite of enzymes is more effective to understand the reactivity properties of metal superoxide complexes.