Single atom-metallic particle interaction enhances the catalytic stability for oxygen reduction reaction (ORR). However, its related mechanism has not been fully understood. Herein, the interaction between a single atom site and metallic particles and its effect on promoting catalyst stability was quantitatively described, taking the example of a single atom of Fe. Metallic particles, as electron donors, decreased the Fe valence by increasing the electron density at the FeN4 position. Subsequently, this strengthened the Fe-N bond and inhibited the electrochemical Fe dissolution, boosting the catalyst stability. Different metals (like Pt, Pd, Au, Ag, Fe, Co, and Ni), existence forms (like particle size, distance, and crystallinity), and content strengthen the Fe-N bond to different extents. A linear correlation between Fe valence, Fe-N bond strength, and electrochemical Fe dissolution amount in single atom-particle catalyst systems experimentally and theoretically supported this mechanism. Consequently, a stable particle-assisted Fe-based ORR catalyst that could operate stably up to 430 h in a direct methanol fuel cell (DMFC) was screened, ranking among the best non-precious ORR catalysts. This study helps to develop cheap yet stable catalysts for fuel cell applications.