The invention discloses a system and a method applied to dry desulfurization and denitrification of flue gas in a coal-fired power plant. The system comprises a desulfurization absorption system, a denitrification reduction system, an activated coke regeneration system, an activated coke conveying system, a flue gas system and an ammonia mixing system, wherein the desulfurization absorption system is a desulfurization tower filled with activated coke, the denitrification reduction system is a denitrification tower filled with a carbon-based catalyst, and the activated coke regeneration system is an activated coke regeneration tower; the activated coke conveying system comprises a first conveying system and a second conveying system, the first conveying system is used for conveying absorbed activated coke to the regeneration tower from the desulfurization tower, and the second conveying system is used for conveying activated coke regenerated by the regeneration tower to the desulfurization tower from the regeneration tower; the flue gas system comprises a flue gas fan for conveying flue gas to a flue gas inlet of the desulfurization tower; the ammonia mixing system comprises a first ammonia mixing system and a second ammonia mixing system which are used for mixing ammonia gas into flue gas. The system and the method disclosed by the invention achieve desulfurization and denitrification of the flue gas, separate desulfurization from denitrification, performs desulfurization at first and then denitrification and guarantees synergistic and high-efficiency desulfurization and denitrification.