It is of great significance for the improvement and utilization of fly ash to reduce the accumulation pollution of coal based solid waste. In this work, a porous high-content iron fly ash sorbent named KIFA was obtained via CaO hydration, addition of pore-making agent and binder, and oxidation modification by NaClO. This sorbent KIFA with an optimized pore structure can promote the formation of K2FeO4. The fixed-bed evaluation results show that the KIFA has the maximum SO2 removal ability at 700 ℃, 5% O2 and 500 mg/m3 SO2, and the breakthrough time and sulfur capacity of the removal efficiency of > 93% are 111.8 min and 93.58 mg/g, respectively, having the ultra-low emission standard of 35 mg/m3. According to the characterization results of fresh and used KIFA, K2FeO4 is a main active component in removing SO2 by KIFA, and Fe(VI) provides the oxidation site, which oxidizes SO2 to SO42-. NO can promote the forward desulfurization reaction. NO, SO2 and CaO can form an intermediate product of NO3SO3Ca, which can be converted into SO42-, thus improving the removal efficiency of SO2.