We investigate the formation of aqueous hydrogen peroxide (H2O2aq) in a DC discharge plasma-liquid system with liquid as the anode. The theoretical analysis and experimental results show that the H2O2aq formation process is mostly controlled by the aqueous electron-induced reactions in the liquid zone directly affected by the plasma. It is shown that the low H2O2aq yield in this system is caused by quenching the dissolved OH radicals through aqueous electrons and alkalization in the plasma-directly-affected liquid zone.