Abstract: This study investigates the impact of flow field distribution on optical transmission characteristics in complex cavities containing optical components under high-speed airflow conditions. A straight cylindrical cavity model incorporating a collimating system and mechanical support structures is established. Numerical simulations combining the Navier-Stokes equations and the k-ε turbulence model are conducted to analyze density distributions under varying temperatures and pressures. Refractive index variations are quantified using the Gladstone-Dale relation, and their effects on optical path difference (OPD) and phase delay are evaluated. Results demonstrate that when the airflow velocity exceeds Mach 0.3, gas compressibility effects become significant, with support structures inducing localized velocity reduction and non-uniform density/refractive index distributions. Lower temperatures or higher pressures amplify density and refractive index magnitudes, increasing the root mean square (RMS) values of phase while maintaining similar spatial patterns. Supersonic flow conditions (Mach > 1) exacerbate refractive index fluctuations and phase distortion. The research reveals the coupling mechanism between high-speed flow fields and optical transmission in complex cavities, providing theoretical insights for cavity design in high-power laser systems. Integrated control of temperature, pressure, and airflow velocity is emphasized to optimize beam quality.