Abstract: In order to find a lightweight solution for the box girders of cranes, taking bamboo as the bionics objective, a structure optimization was made for the transverse stiffeners of the upright rail box girder. A study on the relationship between the nature distribution of bamboo structural parameters and its mechanical behaviors reflects that different cross sections correspond to different equivalent distances between two adjacent nodes of stems. The effect of distances between two adjacent stiffeners on the structure rigidity and strength index was then analyzed to set the maximum distances between two adjacent stiffeners, and the optimization strategy was built to make the stiffener be of the changeable distance and same stability. Finally, the iterative optimization of the elastic buckling analysis was done by the finite element method to complete the solution for stiffeners with changeable distances and the same stability. The results show that the optimization speed increases with the deviation rate increasing. As compared with the traditional box girder, the number of stiffeners in the bionics box girder decreases from 15 to 10, which makes the mass of two main girders decrease 136.12 kg. Besides, the bionics box girder has a more uniform critical buckling load on each section, and meets the design requirements in rigidity and strength index.