To address the challenges posed by the complex flow field structure and unclear aerodynamic characteristics resulting from high-speed inflow and jet interference during rocket sled tests, this study establishes a high-precision numerical prediction method for the aerodynamic characteristics of rocket nozzles based on ground effect-jet-flow coupling. A standard experimental model of a rocket nozzle is selected to validate the reliability of the developed high-precision numerical simulation method for jet-flow coupling. A multi-nozzle thrust engine model is constructed based on the target thrust, systematically investigating the aerodynamic and thrust characteristics of the rocket sled with varying numbers of rocket nozzle jet flow fields under stationary and high-speed motion conditions, while considering the interference of ground effects. Finally, the designed nozzle model is assembled onto a real rocket sled configuration, and the aerodynamic characteristics of the jet flow at high-speed conditions are computed using the developed high-precision numerical simulation method.