The design of combustor has long been the most challenging portion in the design process of a gas turbine. This paper focused on the conceptual design methodology for aircraft combustors. The necessity of this work arose from an urgent need for a comprehensive model that can quickly provide data in the initial phases (conceptual design and preliminary design) of the design process. The proposed methodology integrated the performance and the design of combustors. To accomplish this, a computer code has been developed based on the design procedures. The design model could provide the combustor geometry and the combustor performance. Based on the available inputs data in the initial phases of the design process, a chemical reactor network (CRN) approach is selected to model the combustion with a detailed chemistry. In this way, three different chemical mechanisms are studied for Jet-A aviation fuel. Furthermore, the droplet evaporation for liquid fuel and the non-uniformity in the fuel-air mixture are modelled. The results of a developed design tool are compared with data of an annular engine’s combustor. The results have good agreement with the actual geometry and outputs of engine test rig emissions.