The miniaturization and thinning of high-temperature co-fired ceramics (HTCC) present challenges for maintaining mechanical properties, which is critical for packaging reliability. This study employed direct ink writing (DIW) technology to fabricate alumina HTCC structures with varying interlayer deflection angles, resulting in improved mechanical performance. By incorporating only 3 wt% of organic additives, we developed a water-based alumina slurry with 86 wt% solid content that exhibits shear-thinning behavior. Our results demonstrate that the mechanical properties peak when the interlayer deflection angle is 15°, though this configuration exhibits a higher degree of anisotropy. Conversely, a 90° deflection angle minimizes anisotropy. This work elucidates how different printing filling methods influence the mechanical properties of alumina HTCC and offers valuable insights and experimental evidence for enhancing the mechanical performance of 3D-printed HTCC materials.