The hydrodynamic cavitation abrasive finishing (HCAF) technology, as an innovative, clean, and efficient polishing method, has been proven effective for processing the internal surfaces of additive manufacturing flow channels. However, in-depth mechanistic studies on the key factors affecting the cavitation intensity in the HCAF processing remain limited, even though they play a crucial role in optimizing polishing performance and enhancing process stability. This study aims to apply the HCAF process to the flow channels fabricated by the laser powder bed fusion (LPBF). By adjusting the abrasive inlet pressure and throat diameter, the optimal process parameter combination was obtained, resulting in a 90% reduction in surface roughness near the inlet. fluent simulations and high-speed imaging were conducted to further validate its effect on the cavitation intensity. Furthermore, the channel diameter was found to have a significant impact on the polishing performance. Additionally, predictions of cavitation intensity were used to guide the application of the HCAF polishing for channels of different diameters. The results indicate that although the abrasive inlet pressure has a minor effect on the incipient cavitation number, it significantly alters the pressure distribution in the mixed-flow chamber, thereby influencing cavitation dynamics. The high-pressure region accelerates cavitation bubble contraction and collapse, significantly reducing bubble lifespan and weakening both the intensity and persistence of the cavitation effect. This instability makes sustained cavitation enhancement in the HCAF difficult, affecting material removal efficiency and jet stability. Therefore, the abrasive inlet pressure plays a crucial role in controlling cavitation behavior and enhancing machining performance.