Development efforts to reduce pollutants such as NOx and CO produced by fossil-fuelled systems such as gas turbine engines have become a necessity. The realisation of these efforts in conceptual and detailed design phases before production is very important in terms of reducing the time and costs of the projects. In spite of rapid computer technology development, it is still a difficult and time-consuming process to calculate the minor chemical species such as NOx and CO which are released during the combustion process. In this study, a methodology is proposed to predict the emissions of a reverse flow combustor of a 1000 horsepower turbo-shaft helicopter engine in the design process. In this methodology, the temperature and mass flow values are obtained by computational fluid dynamics (CFD) simulations and the CRN model is constructed by using these values. A MATLAB based tool was developed for chemical reactor network (CRN) modelling. And obtained results were compared with empirical correlations.