Oxy-fuel combustion is considered as one of the most promising options for capturing CO, from coal-fired power plants. Oxy-fuel flue gas contains traces of gaseous elemental mercury (H-g(0)) impurity, which accumulate in the CO, compression units, causing severe damage to the aluminum heat exchangers. It is of great interest that the co-capture of flue gas impurities, such as nitrogen oxide (NOx) and elemental mercury, could be achieved in a CO, compression system at a high pressure. Currently, most of the studies associated with H-g(0) removal were conducted on traditional gas-cleaning devices at atmospheric pressure. It has been demonstrated that both NOx and SO2 from flue gas played a significant role in H-g(0) reactions at atmospheric pressure in O-2/CO2 (oxy-combustion) or O-2/N-2 (air-fired) conditions. However, the effect of those acidic gases on elemental mercury removal in the oxy-fuel compression system at high pressures was unclear. In this work, gas-phase H-g(0) oxidation by NOx and SO2 was experimentally performed at the simulated O-2/N-2 and O-2/CO2 atmospheres at pressures up to 2.5 MPa. It was found that H-g(0) removal was dependent upon the concentration of NO2 in flue gas and primarily achieved by gas-phase reactions between H-g(0) and NO2. High pressure dramatically enhanced the oxidation of NO to NO2. Thus, the flue gas impurity He could be efficiently removed through reacting with NO2 in the CO2 compression purification units. SO2 hardly reacted with H-g(0) but affected the reaction of H-g(0) and NO2. The presence of SO2 inhibited mercury removal especially at high pressures because of the decreased NO2 concentration through the reaction with SO2 and the decomposition of HgO to H-g(0) by SO2. The presence of CO2 made the H-g(0) removal rate less dependent upon the pressure. The removal behavior of H-g(0) in the O-2/CO2 atmosphere was similar to that in the O-2/N-2 atmosphere at pressures lower than 1.0 MPa. With the increasing pressure, the removal rate of He in the O-2/CO2 atmosphere was lower than that in the O-2/N-2 atmosphere.