Based on the motion of yarn carriers on the braiding machine bed

the spatial configuration of interior yarns was analyzed in detail

and a meso-scale model of 4-step three-dimensional (3-D) braided composites was established. In this model

the cross-section deformation

the contact of fiber bundle and the bended centerline due to the mutual squeezing in the braiding process were taken into account. In addition

the structural geometry of the composites was analyzed and the mathematical relationship between the braided parameters and the structure of the unit cell was obtained. The results show that the hypotheses that axis of fiber bundle is curve inside the composites and the section of fiber bundle is oval at control points are close to the real structure and good agreement can be obtained between the calculated and measured values of the geometric characteristics of braided composite samples. The predicted value of unit cell height show that the maximum error remained at about 3%

in addition

when the braided angle is 19°

21° and 21.5°

the prediction results are more close to the measured results. It is suitable for modeling of 3-D braided composites

especially the structure of small braided angle. Therefore

the model presents a foundation for the mechanical properties prediction of the composites.