The work aims to carry out lightweight design to the composite structural packing box so that the structural strength of the box can meet the requirements of internal pressure and stacking conditions. The local non-main load-bearing positions were improved and ABAQUS software was used to conduct numerical simulation analysis on the internal pressure and stacking conditions of the packing box, and the factor of safety for load conditions was 1.5. The theoretical weight reduction of the packing box was 64 kg, and the percentage of weight loss was about 5.4%. Maximum load stress was 344 MPa and deformation was 4.69 mm, meeting the requirements of use. Since the lightweight design of the packing box structure is completed, the stress level of each structure increases slightly under the internal pressure condition, while the stress level of each structure does not change significantly under the stacking condition. In conclusion, the stress level of each structure is within the safe range and will not lead to structural damage. The optimized product has achieved a lightweight effect, and it is proven that the structural improvement is safe and reliable. It can provide data support for the improvement of lightweight structure of similar composite packing boxes in China.