Abstract: A series of cross-section images of three-dimensional (3D) five-directional braided composites were investigated by the charge-coupled device (CCD) microscope，and then the yarn‘s arrangements and their section patterns were discussed. A 3D solid unit cell model was established. The model reasonably reflected the fiber architecture and the cross-section of the yarns. On the basis of the model，the relations between the braiding parameters were determined. The predictions about the dimensions and the fiber volume fractions of preforms show good agreement with experimental results，which provided a basis for finite element analysis (FEA) .