Abstract: The 3-D braiding technique for composites is a new textile technology developed in the United States in the 80 s.The composite of 3-D braided structure is a new kind of composites.Its shock-damage-resistant property,mechanical property and fire-resistant property are fairly good.In this paper,the unit cell geometry of the 3-D braided structure of composites was discussed and the relationships of the structural parameters were established.