This paper studied the yield and release of ClO2 from NaClO2 under various conditions by ultraviolet-visible spectrophotometer (UV-Vis), the existing form of HA-Na under various conditions by Fourier transform infrared spectroscopy (FT-IR), and the reactivity of chlorite/humate (NaClO2/HA-Na) in removal of SO2, NO and Hg-0 under various conditions. The investigated factors included the temperature, the pH, the standing time, the coexistence gases and the anions. The results indicated that the yield and release of ClO2 were significantly affected by the cooperative effects of pH/temperature and pH/standing time. ClO2 was confirmed as an effective oxidant in the removal of NO and Hg-0, and dominated the distribution of Hg2+ in NaClO2 and KCl. SO2 and NO were characterized as the promoters for oxidizing Hg-0 and stabling Hg2+. The addition of Cl-decreased the removal efficiencies of SO2 and NO, but slightly increased the Hg-0 removal efficiency. The best removal efficiencies of SO2, NO and Hg-0 were 100%, 95.3% and 100% respectively. Based on the characterization results by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), the removal products were determined as NaCl, humic (HA), Na2SO4, NaNO3, HgSO4, Hg(NO3)(2) and HgCl2. The reaction mechanism was proposed finally.