The effects of discharge polarity, discharge electrode configuration, O-2/CO2 ratio, and water vapor on the elemental mercury (Hg-0) oxidation in simulated flue gas were investigated in a wire-cylinder plasma reactor energized by DC power. The Hg-0 oxidation efficiency increases with the increase of specific energy density (SED). Compared with the glow corona discharge energized by negative DC high voltage, the streamer corona discharge induced by positive DC high voltage exhibits a much higher Hg-0 oxidation efficiency under identical SED. The discharge electrode configuration significantly influences the energy density in the plasma reactor, but hardly affects Hg oxidation for a fixed SED. The increase of O-2/CO2 ratio in simulated flue gas obviously enhances Hg-0 oxidation. However, with the addition of H2O, Hg-0 oxidation is remarkably restrained due to the decrease of O-3 formation.