The invention provides a system and method for industrial-boiler flue-gas desulfurization and denitrification. The system comprises a spraying tower, a pre-positive oxidation system arranged on an inlet flue of the outside of the spraying tower, a desulfurization cycling system, a gas-liquid separation layer and a denitrification cycling system, wherein the desulfurization cycling system, the gas-liquid separation layer and the denitrification cycling system are arranged inside the spraying tower. The method includes the steps of preposition oxidation, desulfuration treatment and denitrification treatment. According to the system, oxidation-method denitrification and oxidation cost and power consumption are reduced, absorption efficiency is improved, recycling of a catalyst is achieved, the problem that products cannot be treated in oxidation-method denitrification is solved, and the system provides a feasible technical proposal for simultaneous desulfurization and denitrification of industrial flue gas. According to the method, a desulfurization spraying layer and a denitrification spraying layer which are located inside the spraying tower is partitioned through a gas-liquid separation device, and therefore it is completed that desulfurization and denitrification are simultaneously conducted; in the method, flue-gas denitrification treatment is conducted based on a phospholipid organic catalyst and a regenerant which are used in a wet desulphurization system, and recycling of the denitrification is conducted with an off-line regenerated catalyst.