In this paper the numerical simulation of a high swirled confined natural gas diffusion flames are studied. Several factors influencing the combustion process are examined. One of the goals is to study the influence of the turbulence models and the reaction mechanism on the prediction of the flow, temperature fields and modelling of NOx emissions. The numerical calculation has been performed using the commercial code Fluent. The standard k-ε and RSM models are used to describe the turbulent flow. The Eddy dissipation model (6 species and 2 reactions) and a chemical equilibrium model in conjunction with (β function) PDF model (9 species and 8 reactions) are used to model the turbulence-chemistry interaction. A NOx post-processor has been used for predicting NO emissions from combustors. The concentration of O and OH radicals are obtained assuming the partial-equilibrium assumption and using a PDF in terms of temperature. The comparison of the numerical results with the available experimental data shows a satisfactory agreement.