The work aims to set up the plateau stress expression based on folding of hole wall by considering the energy dissipation mechanism for folding of slant hole wall of honeycomb core. First, the energy dissipation of horizontal fixing plastic hinge of deformed units of honeycomb core was analyzed theoretically; then, crosswise in-plane compression tests were carried out on honeycomb cores under different thickness-span ratios to acquire the plateau stress; finally, the test results were compared with Gibson & Ashby model and the proposed model. The ratio of thickness of honeycomb cell wall to side length of honeycomb cell element had certain influence on the plateau stress. The honeycomb core in-plane compression plateau stress was proportional to the square of the ratio of cell wall thickness to side length of honeycomb cell element. Based on the comparison results, the theoretical value of the proposed model and the test value of plateau stress were more identical. It reveals the energy dissipation mechanism of honeycomb core crosswise in-plane compression. The plateau stress expression can be applied in the evaluation of mechanical property of double-wall thick honeycomb in-plane compression of various materials, and thus has certain universality.