To address surface quality defects caused by traditional mechanical polishing of gears, such as machining scratches and large surface waviness, this study proposes a novel immersed chemical-mechanical polishing (CMP) process for gear finishing. Numerical simulations were conducted in FLUENT to analyze the gear surface stress distribution and polishing fluid flow trajectories under different process conditions. The Euler–Euler method and RNG k–ε turbulence model were used to optimize process parameters and clarify the formation mechanism of ultra-smooth tooth surfaces. Experimental results for spiral bevel gears show that the proposed immersed CMP process effectively improves surface quality. The tooth profile roughness was reduced from Ra 1.531 μm to 0.509 μm, and surface scratches were significantly alleviated. These results confirm the feasibility and effectiveness of the proposed process. This study provides a reliable approach for efficient and precision polishing of complex-structured gears and extends the application of CMP technology to non-planar mechanical components.