A novel photochemical spray reactor is first developed and is used to remove Hg-0 and simultaneously remove Hg-0/SO2/NO from flue gas by ultraviolet (UV)/H2O2 process. The effects of several parameters (UV wavelength, UV power, H2O2 concentration, Hg-0 inlet concentration, solution temperature, liquid-gas ratio, solution pH, SO2 concentration, NO concentration, and O-2 concentration) on removal of Hg-0 by UV/H2O2 process were investigated. Removal mechanism of Hg-0 is proposed and simultaneous removal of Hg-0, NO, and SO2 is also studied. The results show that the parameters, UV wavelength, UV power, H2O2 concentration, liquid-gas ratio, solution pH, and O-2 concentration, have significant impact on removal of Hg-0. However, the parameters, Hg-0 inlet concentration, solution temperature, SO2 concentration, and NO concentration, only have small effect on removal of Hg-0. Hg2+ is the final product of Hg-0 removal, and Hg-0 is mainly removed by oxidations of H2O2, center dot OH, center dot O, O-3, and photoexcitation of UV. (c) 2014 American Institute of Chemical Engineers AIChE J, 60: 2275-2285, 2014