Systematic experimental research has been conducted in a fix-bed reactor system to determine the impact of coal-fired flue gas species and temperature on mercury oxidation. This work focuses on the temperatures range of 200℃ to 800℃ to demonstrate that temperature is a critical factor for the effect of the gas components on the mercury oxidation process. Among the investigated gases, hydrogen chloride is essential for oxidizing the elemental mercury. Nitrogen oxide was also found to have a positive correlation with the mercury oxidation when hydrogen chloride was present. Sulfur dioxide can either promote or inhibit the oxidation depending on the conditions; however, when nitrogen oxide is also present, sulfur dioxide has a negative impact. Ammonia exhibits an strong inhibitory effect. Several plausible mercury oxidation pathways are suggested in this paper.