After-burning flow fields in ramjet of different inlet modes were numerically simulated using RNG k-ε turbulence model and one-step fast chemical reaction by the SIMPLE method based on unstructured meshes, which was for enhancing the mixed effect of fuel and air in ramjet chamber and improving after-burning efficiency. The distribution of flow field parameters was acquired. The computational results show that fuel and air are better mixed and combustion efficiency is enhanced using one inlet mode and increasing angle of two inlets, and two inlets mode is propitious to thermal protection of chamber. All those provide references to designers.