Numerical 2D simulation and research on internal flow field and external flow field of rocket motor nozzle using FLUENT software. Analyze the flow condition of internal flow field and external flow field, and according to add in the amount of the different gas components, obtain the clear distribution of contour of density flow field, pressure flow field and various material components and so on. Simulation results agree with the results observed from the test on the ground, and provide reference for solid rocket motor development.