To achieve superior advanced oxidation processes (AOPs), transitional state activators are of great significance for the production of active radicals by H2O2, while instability limits their activation efficiency. In this study, density functional theory calculation (DFT) results showed that Cu+ exhibits excellent H2O2 activation performance, with Gibbs free energy change (Delta G) of 33.66 kcal/mol, two times less than that of Cu2+ (77.83 kcal/mol). Meanwhile, an electro-Fenton system using Cu plate as an anode was proposed for in situ generation of Cu+. The released Cu with low-valence state can be well-confined on the surface of the exciting electrode, which was confirmed by X-ray photoelectron spectroscopy (XPS), Raman, and UV-vis spectroscopy. The hydroxyl radicals in this Cu-based electro-Fenton system were determined by the electron spin resonance (ESR). The nitrobenzene degradation ratio was greatly increased by 43.90% with the introduction of the proposed in situ electrochemical Cu+ generation process. Various characterization results indicated that the production of Cu+ was the key factor in the highly efficient Cu-based electro-Fenton reaction.