Discharge plasma–liquid systems provide an interesting research field for many physical and chemical processes. These fascinating processes can be studied by using systems with liquid as anode and cathode, and the yield of aqueous hydrogen peroxide (H2O2aq) in the plasma–liquid system with the liquid anode is significantly lower than that with the liquid cathode. We improve the H2O2aq yield in the plasma–liquid system with the liquid anode by adding appropriate amount of ethanol in the liquid. A seven-time increase in the production rate is reached when the ethanol volume concentration is 5%, while further increase in the ethanol concentration will decrease the production rate. The H2O2aq production improvement is ascribed to the atomic oxygen-induced hydrogen abstraction reactions from ethanol which in situ improve the concentration of the H2O2 building brick, the OH radicals, in the liquid. However, excessive ethanol can scavenge the in situ formed OH radicals through the hydrogen abstraction reaction, by which the H2O2aq formation is inhibited.