The invention discloses a method and system for removing reductive substances from carbide slag slurry in a carbide slag desulfurization process. According to the carbide slag desulfurization process,the carbide slag slurry is adopted as a desulfurizer to circulate in a desulfurization absorption tower along with circulating slurry so as to desulfurize flue gas. The method comprises the followingsteps: the circulating slurry is added into the carbide slag slurry, and meanwhile hydrogen peroxide is further added into the circulating slurry to oxidize the reductive substances in the carbide slag slurry. The hydrogen peroxide and the carbide slag slurry are added into the circulating slurry together, in the process that hydrogen peroxide and the carbide slag slurry make full contact with the circulating slurry to be mixed, the hydrogen peroxide is utilized to oxidize the reductive substances, dissolved in water, in the carbide slag slurry, after the reductive substances are oxidized bythe hydrogen peroxide in advance, the phenomena that the reductive substances make contact with a desulfurization product, namely calcium sulfite, the surface of the calcium sulfite is wrapped with the reductive substances, consequently the oxidation time of the calcium sulfate is too long, and even oxidizing cannot be conducted can be prevented, and thus the oxidation efficiency of the desulfurized slurry can be improved.