We comparatively study two representative ballistic transport models of nanowire metal-oxide-semiconductor field effect transistors,i.e.the Natori model and the Jiménez model.The limitations and applicability of both the models are discussed.Then the Jiménez model is extended to include atomic dispersion relations and is compared with the Natori model from the aspects of ballistic current and quantum capacitance.It is found that the Jiménez model can produce similar results compared with the more complex Natori model even at very small nanowire dimensions.