The invention discloses a method for enhancing the activity of calcium sulfite slurry in a wet flue gas denitration technique, which utilizes the calcium sulfite slurry to absorb nitric oxide; and the calcium sulfite slurry is added with additive which can be soluble sulfate or soluble magnesium salt. The added additive leads the solubility of calcium sulfite to be obviously improved, and enhances the activity of the slurry, thus not only greatly improving the denitration efficiency, but also being beneficial to the oxidation of the calcium sulfite. The method enhances the denitration feasibility of the calcium sulfite, saves the cost of forced oxidation in the desulphurization process, and realizes the organic combination between wet desulphurization and wet denitration.