An electrochemical reactor has been developed for the on-site electrochemical production of hydrogen peroxide. Comparison was made between a trickle-bed mode where gas and liquid phases flowed downward cocurrently in the graphite-felt cathode and a packed-bed mode where two phases flowed upward cocurrently. At the same now condition of gas-liquid phase, the current efficiency Ce using the trickle-bed electrode was higher than that using the packed-bed electrode with gas-sparging. Mathematical analysis based on a three-phase bed model was made to fit the over-potential profiles in the cathode by using electrode kinetics and mass-transfer parameters, gas and liquid holdups in the bed, the effective conductivity of the solution phase and the effective surface area of electrode. The current efficiency Cc was affected by now rates of gas and liquid, and the current density, because of the changes in the effective specific surface area a(eff) of electrode and liquid-solid mass transfer coefficient k(mA) or oxygen onto the electrode. In this experiment, Ce was increased mainly by increasing a(eff) rather than k(mA). Using the trickle-bed electrode, a(eff) and k(mA) were higher than that using the packed-bed electrode, because oxygen gas and catholyte were dispersed uniformly in the cathode compartment, thus leading to higher Ce.