Abstract: To accurately characterize the random roughness of the inner walls of aerospace engine nozzles, a three-dimensional Gaussian random rough-surface modeling method based on Monte Carlo simulation was developed. Numerical simulations were performed on a typical nozzle with three roughness levels (Ra1.6, Ra0.8, and Ra0.4) to systematically analyze their effects on cavitating flow. The results showed that as the surface roughness decreased, the cavitation region extended further in the axial direction, while its radial scale and intensity diminished. Rough surfaces induced larger low-pressure zones at the inlet corner, where microscopic concavities served as nucleation sites for micro-cavitation. The peak internal flow velocity increased with roughness, whereas the outlet velocity and total mass flow rate remained nearly unchanged. Analysis of turbulent kinetic energy revealed that increasing roughness enhanced near-wall turbulence, thereby promoting local pressure reduction and cavitation inception. This study demonstrates that surface roughness regulates the internal flow mainly through local flow structures rather than macroscopic performance, providing a theoretical basis for optimizing the design and manufacturing tolerances of liquid rocket engine nozzles.