Experimental and theoretical studies have been performed to explore NOx reduction by CH4 without the presence of oxygen. GRI-Mech 3.0 is proved to be valid for modeling NOx abatement by injection of methane and the agreement is within 20%. The NO can be reduced to nitrogen intermediates only with CH4 converted into CHi, which initially results from thermal decomposition of CH4. The nitrogen intermediates are subsequently converted into N2 or NO depending on the reaction conditions. The impact of temperature and CH4 to NO ratio on NOx reduction is also investigated. The increase of temperature and CH4 to NO ratio induces a significant increase of NOx reduction efficiency. But extremely high temperature, i.e., above 1400°C, has an adverse effect on NOx reduction. The oxygen concentration has a remarkable effect on NOx reduction and injection of CH4 into regions characterized by reducing atmosphere and high temperature stimulates the NO reduction process.