The invention relates to an alkaline process desulfurization system which comprises a sodium alkali supply system, a desulfurization and dust collection integral system and a gypsum slurry treatment system. The alkaline process desulfurization system is applicable to a mating boiler unit flue gas treatment system of a paper making plant, a reducer for desulfurization is provided by using a sodiumalkali tank in mating a boiler power plant of the paper making plant, and a limestone system can be replaced. Desulfurization wastewater is treated in a water pond of a factory. Sodium hydroxide or sodium carbonate is adopted as an absorber to absorb SO2 in a flue gas, then an absorption liquid with sodium sulfite and sodium hydrogen sulfite is generated, high absorption efficiency is achieved forSO2 in the flue gas, and a good desulfurization effect is achieved; and a common limestone-gypsum desulfurization system is simplified, and the system provided by the invention is simple, convenientto repair and capable of saving energy and reducing energy consumption.