Today when preparing a CFD study, there is a need to make a compromise between the results accuracy (applied models) and the computational cost. In this study the non-premixed equilibrium combustion model is assessed by a comparative numerical method, when applied to diffusion type gas microturbine combustor methane powered. In order to make it, a diffusion type gas microturbine combustor methane powered simulation was done twice, using one time the non-premixed equilibrium combustion model and second time the steady diffusion flamelet combustion model (with the use of Gri-Mech 3.0 mechanism), which is suitable for this specific application. The thermal operation parameters of both simulations were compared and their analysis shown that equilibrium model permits to obtains accurate thermal results, compared to more complex and accurate combustion model as the steady diffusion flamelet model.