This study examines the influence of yarn reduction-specifically the number of layers and their location on the low-velocity impact response and post-impact compression performance of 3D woven composites. Specimens with yarn reduction on either the upper or lower surface were impacted at two different energy levels. Damage evaluation was conducted using C-scan, µ-CT, and DIC methods. The results indicate that yarn reduction on the lower surface leads to notable reductions in initial stiffness and peak load, with a clear threshold effect when two or more layers are reduced. This condition also resulted in significantly expanded damage area. In contrast, reduction on the upper surface mainly increased energy absorption and permanent displacement under high-energy impact. Additionally, compression-after-impact strength was lower for specimens with yarn reduction on the lower surface, where failure was governed by a damage network initiated by the yarn reduction. These findings offer valuable guidance for designing damage-tolerant composites with yarn reduction.