Abstract: Chemical speciation and distribution of mercury in the flue gas were studied in a small-scale coal-fired boiler with wet flue gas precipitator and desulfurization(WFGPD) system of Guiyang.In the flue gas cleaned by the WFGPD system,the percentage of Hgp,Hg2+ and Hg0 with regard to Hgt were 10.4%,6.0%,83.6%,respectively.The removal efficiency of Hg2+ (87.9%) and Hgp (76.1%)by the WFGPD system were higher than that of Hg0(30.4%).The total output mercury of this boiler is a little higher than the total input mercury of the boiler because of statistical error of the fired coal per year and the Ontario Hydro sampling-analytical error of mercury in flue gas.The ratio of output Hgt to input Hgt is 103.6%～107.4%.The mercury emission factors were that:41.7% of Hgt was found in clinkers and 65.7% of Hgt entered into flue gas before the WFGDP system.When the flue gas was cleaned by the WFGDP system,only 25.05% Hgt was emitted to the atmosphere, 26.7% Hgt discharged into the water and 7.8% Hgt into the cinder.