Abstract: Composite sandwich structure with carbon fiber reinforced polymer (CFRP) square honeycomb core was designed and fabricated using the interlocking method. The out-of-plane compressive performance and the three-point bending performance of the sandwich structure were studied experimentally. The failure modes of the sandwich structure under out-of-plane compressive loading were obtained and the failure mechanism and energy absorption characteristics were analyzed. The influences of the asymmetry of the face sheet quality and the direction of the slots on the failure modes and bending strength of the sandwich beam under three-point bending loading were explored, respectively. The experimental results show that the sandwich structure under out-of-plane compressive loading exhibits the progressive failure mode: fiber fracture near the slots, bucking and fracture of the slotted part of ribs, and the fracture and crushing of the unslotted part of ribs. The compressive stress-strain curve has obvious two-stage plateau stress, which means the excellent energy absorption characteristics of the sandwich structure. The sandwich structure has the higher load-carrying capacity and initial failure loading for the thicker upper face sheet and the upward slots of the long ribs of the core.