<p>Carbon fiber-reinforced silicon carbide (C/SiC) composites are extensively employed in aerospace applications owing to their high-temperature strength, low density, and thermal stability. However, conventional machining of these hard and brittle materials is hindered by severe tool wear, low processing efficiency, and high operational costs. As a non-contact and tool-wear-free technique, abrasive waterjet (AWJ) machining enables efficient bulk material removal and can function as a roughing process that complements conventional finishing operations to ensure dimensional accuracy. In this study, AWJ milling was systematically investigated to elucidate how fiber orientation and jet parameters influenced material-removal behavior and surface integrity. Experiments were conducted on a five-axis AWJ system at traverse speeds ranging from 2 000 mm/min to 4 000 mm/min and standoff distances between 6 mm and 18 mm. Scanning electron microscopy (SEM), white-light interferometry, and depth-profilometry identified three orientation-dependent fiber-damage modes—splitting and pull-out in warp yarns, circumferential fracture in weft yarns, and protrusion-bending in needled fibers—originating from crack deflection and fiber-matrix interfacial debonding under localized jet loading. An increase in standoff distance broadened the kerf width while reducing the maximum removal depth by approximately 50%, owing to jet energy dissipation and the transition of the profile geometry from U-shaped to V-shaped. Elevated traverse speeds shortened the effective jet-material interaction time, reducing surface roughness from 305.6 µm to 167.8 µm while suppressing excessive erosion and interfacial delamination. These findings establish a mechanistic framework for predicting AWJ milling depth and defect evolution in architectured C/SiC composites, thereby providing practical guidance for high-precision, dust-free machining of aerospace thermal protection components.</p>