Benefiting from the merits of d-block and p-block elemental single-atom catalysts (SACs), p–d hybridized SACs with atomically dispersed d-block catalytic sites periodically confined within the p-block-element represent a distinct development in the realm of highly efficient and low-cost SACs, which can not only effectively stabilize the single-atom reactive sites from clustering, but also practically maximize the utilization of the metal atoms to 100%. Here, based on density functional theorycalculations, taking two-dimensional metal–organic frameworks (2D-MOFs) TM₃(C₆O₆)₂ (TM = Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, Ag, Pt, Au) as typical examples for p–d hybridized SAC platforms, we establish an intriguing synergetic charge transfer mechanism involved among the periodically confined d-block hosting TM active sites and p-block non-metal elements in the MOF structure for O₂ activation and CO oxidization. Specifically, for the key step of O₂ adsorption and activation, except for hosting d-block TM active sites, the second-nearest neighbouring p-block C atoms may dominate or donate significant charge via the bridge of the nearest neighbouring substrate O atoms, which effectively reduces the CO oxidization barriers to the range of 0.23–0.60 eV for most TM₃(C₆O₆)₂. These findings are constructive for designing highly efficient and low-cost p- and d-block hybridized SAC systems.