The utility model relates to the technical field of alkali production coal-fired furnace flue gas treatment, and discloses a flue gas purification system which comprises a denitration device and a desulfurization device, the denitration device comprises a flue gas channel, the flue gas channel is communicated with a waste heat boiler, and a gas outlet of the waste heat boiler is communicated witha gas inlet of a denitration reactor; the desulfurization device comprises a desulfurization tower, a gas inlet of the desulfurization tower is connected with a gas outlet of the denitration reactor,and a gas outlet of the desulfurization tower is connected with a chimney. The flue gas channel is communicated with the ammonia water evaporation tank, ammonia water is converted into a gas state from a liquid state through waste heat of flue gas, and at least one layer of reaction plate with a catalyst is arranged in the denitration reactor, so that complete denitration of the flue gas is guaranteed; at least one layer of alkaline desulfurization liquid spraying mechanism is arranged in the desulfurization tower to guarantee the desulfurization effect, the demisting mechanism further purifies the desulfurized flue gas, it is guaranteed that the flue gas entering the chimney is completely purified, and safety and environmental protection are achieved.