Abstract: Crop stems are composed of multi-scale structures such as cells, tissues, and organs. Vascular bundle is the main mechanical supporting tissue of the stem. Cell is the basic mechanical supporting unit. The mechanical properties of cells depend on the mechanical properties of the cell wall and the morphological structure of the cells. The structural characteristics of the cell wall affect the mechanical properties of the cell, vascular bundle, and stem step by step. The study of cell wall structure characteristics can provide a reference for breeding varieties with good lodging resistance. In this study, the microfibril angle of sclerenchyma cell wall of sugarcane（Saccharum officinarum） variety ‘Guitang No.49’ vascular bundles of sugarcane stems was tested by X-ray diffraction technology. The effects of microfibril angle and crystal size on the mechanical properties of the vascular bundles of sugarcane stem were analyzed. The internal relationship between the ultrastructure and macroscopic mechanical properties of sugarcane was studied. The results showed that in the cross section of stalk, in the direction from skin to core, the microfibril angle of sclerenchyma cells increased. Along the stalk from its base, middle to top the microfibril angle of thick-walled cell wall did not change significantly. The tensile elastic modulus of a single vascular bundle of the stem was strong negative correlation with the microfibril angle. Its correlation coefficient r=-0.655. The tensile elastic modulus was strong positive correlation with the cellulose crystal size. Its correlation coefficient r=0.604.About 43% of the difference in tensile strength of a single vascular bundle was caused by the microfibril angle.