A method for simultaneous removal of SO2, NO2 and NO from coal-fired flue gas by sodium humate (HA-Na) solution was proposed. The effects of various influencing factors on the simultaneous removal were investigated systematically, such as the concentration of HA-Na, the reaction temperature, the pH of HA-Na solution and the coexistence gases in the simulated flue gas. The experimental results indicated that the desulfurization efficiency was constant at 100% in almost all tests, whereas the removal of NO2 and NO was significantly affected by the reaction temperature, the pH of HA-Na solution and the coexistence gases. SO2 was characterized as either promotion or inhibition on NO removal, depending on the concentration. NO2 and O-2 as two gas oxidants can promote NO removal. However, the introduced CO2 will compete with SO2 and NOx for HA-Na, which results in a decrease of simultaneous removal. Under the established optimal reaction conditions, the simultaneous removal efficiencies of 100% for SO2, 99.6% for NO2 and 65% for NO were obtained. The main products were identified as humic acid (HA), sulfate, nitrite and nitrate based on the characterizations by FT-IR, XRD, IC and EDX. (C) 2015 Elsevier B.V. All rights reserved.