In order to clarify the destination of S and N elements in the ozone cascade oxidation absorption process, improve the desulfurization and denitrification efficiency of the system and the reuse quality of by-products, and reduce the emission of SO₂ and NO_x in the sintering flue gas, the ozone cascade oxidation is used combined with calcium-dense coherent tower absorption process to desulfurize and denitrify at the same time, research the balance of S and N in the desulfurization and denitrification of iron and steel sintering flue gas in the ozone cascade oxidation absorption process, and monitor the mass concentration of SO₂ and NO_x before and after the desulfurization and denitrification system through the CEMS flue gas continuous monitoring system, the mass fractions of S and N elements are detected by elemental analysis and ion chromatography, and the mass fractions of phase analysis and CaSO₃ are detected by XRD and iodometry. The results show that the removal efficiency of SO₂ and NO_x in the application of iron and steel sintering flue gas desulfurization and denitrification in the application of ozone cascade oxidation absorption process is 99.6% and 88.9%, respectively, the mass concentration of SO₂ at outlet is less than 10 mg/m³, and the mass concentration of NO_x is less than 30 mg/m³, which is significantly lower than the national ultra-low emission standard. The S balance rate before and after system purification is 101.24%, and the N balance rate is 90.25%, indicating that the S and N element patterns of the cascade oxidation absorption process became clear. In addition, the analysis results of the absorption products after purification show that the absorption products discharged by the ozone cascade oxidative absorption process are composed of CaSO₃, CaSO₄ and Ca(OH)₂. Among them, the mass fraction of CaSO3 is significantly lower than the corresponding value of "SCR denitrification + semi-dry desulfurization" process. This shows that the ozone cascade oxidation absorption process is beneficial to the conversion of CaSO₃ to CaSO₄, and improves the desulfurization efficiency of the purification system and the reuse quality of by-products.