The invention relates to a 
system for simultaneous desulfurization-
denitrification-demercuration based on a combination of free radical pre-oxidation and wet absorption. The 
system adopts the structure that 
ultraviolet light and a catalyst are combined to decompose a 
peroxide; during 
decomposition, strong oxidative hydroxy or 
sulfate radical free radical are generated for oxidative removal of SO2, 
NOx and Hg0 in an 
impact bed; part of 
flue gas from an emission source and part of catalyst particles are mixed and sprayed into the 
impact bed through high-speed nozzles, and the other part of 
flue gas and catalyst particle are mixed and sprayed into the 
impact bed through the high-speed nozzles which are coaxially arranged in an opposite manner; meanwhile, a 
peroxide solution is sprayed into the impact bed through sprayers, so that such three gas steams are subjected to impact and mixing in the impact bed. The 
system has the advantages that the 
ultraviolet light and the catalyst are combined to decompose the 
peroxide, strong oxidative hydroxy or 
sulfate radical free radical are generated for oxidation of SO2, 
NOx and Hg0, so that gas-sate 
divalent mercury, 
nitrogen dioxide, 
sulfur trioxide, 
sulfuric acid and 
nitric acid are generated, and then SO2, 
NOx and Hg0 are removed in a wet desulfurization system at the 
tail part. Therefore, the system provided by the invention can be used for transforming the conventional 
coal burning boiler to achieve 
sulfur-
nitrogen-mercury integrated removal, and has a broad market application prospect.