To investigate the plume flowfield and thermal environment of heavy-lift launch vehicles, a numerical model for a nine-nozzle launch vehicle was established based on the three-dimensional compressible Navier–Stokes equations, the Realizable [Formula: see text] turbulence model, the DOM radiation model, and a finite-rate chemical kinetics model. The study indicates that as the rocket ascends, the compressive effect of the external environment on the exhaust plumes gradually diminishes. Multiple p