CFRP (carbon fiber reinforced composites)/honeycomb sandwich structures are widely used in aerospace, automotive, and high-speed rail industries due to their excellent mechanical properties and lightweight characteristics. This study investigates the impact of three designed toughened interfaces on the three-point bending performance of honeycomb structures. The results show that introducing a multiscale toughened interface made of poly(p-phenylene benzobisoxazole) (PBO) fibers grafted with polydopamine (PDA) and multi-walled carbon nanotubes (CNT) increases the peak load and post-peak load of the sandwich structure by 49.7 % and 51.9 %, respectively, and the absorbed energy by 92.4 %. This toughened interface adjusts the stress relationship between the panel, interface, and honeycomb, altering the deformation process and crack propagation mode of the sandwich structure. The micro-nano fibers form fiber bridging at the interface, changing the crack extension mode between the interfaces, transforming the delamination from a single debonding to the combined action of plate core debonding and honeycomb core buckling. Additionally, experimental results show that PBO fibers treated with PDA and CNT exhibit significantly improved surface roughness, Surface area per unit mass, wettability, and tensile strength, which delay and prevent crack propagation at the interface, effectively reducing panel debonding at the bonded joints.