The multi-cell-wall honeycomb structure was introduced into the stiffened plate design. Based on the load-bearing method of the three-point bending experiment, the wall thickness and porosity of the honeycomb cells were designed in a gradient form. The specimens were manufactured by 3D printing technology, and the materials was polylactic acid. Through experimental testing and finite element analysis, the influence of gradient form, cell direction and bearing position on the structure's bearing performance was studied, and the stiffened layer was optimized based on the results. The results show that: the gradient form of wall thickness, the vertical direction of the cell and the closeness of the indenter axis to the horizontal direction can all improve the structural bearing performance; the optimization to stiffened layer can significantly improve the utilization rate of the materials. In addition, the specimens under different bearing positions have different destruction modes.