Abstract: To overcome the limitations of 3D spacer composites, including simplistic core structure design, the global instability of core piles, and the difficulty in balancing high strength and thermal insulation, this study reports a core-weft interlaced 3D spacer composite structure. By redesigning the weave structure of the basic 3D spacer preform and optimizing the shedding and weft insertion process, stable and efficient fabrication of the core-weft interlaced preform was achieved. The compressive behaviors and thermal insulation mechanism of 3D spacer composites (SC), half core-weft interlaced 3D spacer composites (HCWISC), and core-weft interlaced 3D spacer composites (CWISC) were investigated. The results demonstrate that the core piles of the CWISC form bonded support points in the warp direction, causing the failure mode to transform from global instability to the reverse tilting of half-height core piles, which shows the fishbone shaped failure morphology. The compressive strength and specific energy absorption of the CWISC reached 1.62 MPa and 350.8 kJ⋅m⁻³, respectively, which are 149% and 226% higher than those of SC. The introduction of the core-weft increases the complexity of the core cavity and the geometric length of the core piles in CWISC, effectively suppressing heat convection and increasing the thermal resistance of heat conduction. Under heating at 120℃, the surface temperature of CWISC is only 50.9℃. The core-weft interlaced spacer structure provides a novel technical approach for regulating the geometric morphology and optimizing the performance of core piles, offering a process reference for the design and application of high-performance lightweight spacer composites.