To address the poor surface quality and non-uniform polishing in internal micro-channels of additively manufactured components， where traditional finishing methods are inapplicable and unidirectional processing exhibits limitations， this study adopts a bidirectional finishing mode. Combining simulation and experimentation， it systematically investigates the effects of water-based silicon carbide （SiC） and alumina （Al?O?） abrasives on hole enlargement uniformity， surface roughness， and surface morphology under both unidirectional and bidirectional processing conditions. Results demonstrate that bidirectional processing significantly improves polishing uniformity compared with unidirectional processing. Specifically， the difference in hole enlargement between inlet and outlet is reduced from 51 μm to 27 μm using SiC abrasives， and from 40 μm to 20 μm using Al₂O₃ abrasives. Furthermore， bidirectional processing markedly reduces and homogenizes surface roughness across all regions： Roughness values in SiC-processed channels decrease to 3.726 （inlet）， 3.612 （outlet）， and 3.639 μm （middle）， while those in Al?O?-processed channels decrease to 4.127 （inlet）， 3.876 （outlet）， and 3.963 μm （middle）. Comparative analysis indicates SiC outperformes Al?O?， yielding channels with an average surface roughness approximately 0.3 μm lower under bidirectional processing （inlet： 0.4 μm lower， outlet： 0.26 μm lower， middle： 0.32 μm lower）.