Abstract: The methodology of add or cut yarns during 3-D braiding courses were analyzed from a viewpoint of unit cell.The process,applicability,advantages and disadvantages of both the unit number reduction and unit size reduction methods were discussed.The apparent structure of the preform was observed by digital photograph,and the yarn tracks of cutting point in surface or inner control unit before and after cutting were obtained by topological analysis.Geometrical models of yarn interlace were built.The research shows that 3-D braided preforms made by these two cutting technologies have no such defect as holes.Yarn incline direction has not changed,and the incline angle changes a little.Therefore,there exists no obvious stress concentration in the whole structure.These methods are suitable,individually or in combination,for braiding section-changed composite products.