Three-point bending experiments were carried out on honeycomb paperboard, and its bending failure mode and process were analyzed based on the structure and force of honeycomb paperboard to investigate the bending failure mode and mechanism of paper honeycomb sandwich structure. It was found that the bending failure modes of honeycomb paperboard mainly included panel buckling and local collapse. The bending failure process of honeycomb paperboard was divided into five stages. The bending failure mode of honeycomb paperboard was related to panel buckling, plastic hinge formation and squeezing towards the center by compression of the honeycomb cell walls.