The performance of the steel scale (SS)-CaO composite on the combustion of coke nuts and in-situ reductionof SO2 and NO emission was investigated. Combustion experiments show that SS-CaO compositeaccelerates coke combustion and reduces SO2 and NO emissions concurrently. X-ray diffraction (XRD),scanning electron microscopy (SEM), and electron spin resonance (ESR) were used to investigate thecatalysis mechanism. Results show that SS and CaO have synergistic effect in in-situ denitration. Theincrease of SS and CaO fraction in the composites improve the denitration and sulfur fixation performance,respectively. The denitration activity is mainly attributed to the Fe2O3 in SS and Ca2Fe2O5 formedduring combustion. The desulfurization is due to the sulfur fixation with CaO. The increasing fraction ofCaO in the composites leads to the agglomeration of ash particles. 2%CaO is confirmed as the optimumaddition for catalytic combustion and emission reduction. This work sheds light on the cheap and effectivecatalysts that are potentially useful for iron ore sintering.