Understanding catalytic mechanisms at the nanoscale is essential for the advancement of lithium-oxygen (Li-O-2) batteries. Using in situ electrochemical atomic force microscopy, we explored the interfacial evolution during the Li-O-2 electrochemical reactions in dimethyl sulfoxide-based electrolyte, further revealing the surface catalytic mechanism of the soluble catalyst 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ). The real-time views showed that during discharge flower-like Li2O2 formed in the electrolyte with DBBQ but small toroid without DBBQ Upon charge, Li2O2 decomposes at a slow rate from bottom to top in the absence of DBBQ yet with an outside-in approach in the presence of DBBQ Bigger discharge products and more efficient decomposition pathways in the DBBQ-containing system reveal the catalytic activity of DBBQ straightforwardly. Our work provides a direct insight into the surface effect of soluble catalyst DBBQ on Li-O-2 reactions at the nanoscale, which is critical for the performance optimization of Li-O-2 batteries.