The CFD software FLUENT was used to simulate the flow in the 2D asymmetric ramp-nozzle.The effect of four widely used turbulent models and three kinds of grid density on the numerical results were discussed.All the numerical results are compared with the experimental data published by NASA and agree with each other very well.It shows that FLUENT software with medium grid density and RNG k-ε model can quickly yield accurate result,so it is very suitable for the internal and external flow simulation of a 2D asymmetric ramp nozzle with hypersonic free stream.