Abstract: The longitudinal tensile tests were conducted on the 3-D braided composites with various yarn cutting down parameters.The effect of braiding parameters on the tensile properties was discussed,and the failure mechanism of materials was investigated.The results show that when the fiber volume fraction is equivalent,cutting down of yarns reduces the strength of the composites,but has little effect on the initial modulus.The defective point resulted from yarn cutting down has small influence on tensile property,and the fracture section of samples presents a random characteristic.Lacking yarn in a certain length has more influence on tensile property,and breakage occurs mostly at the yarn lacking section.When yarn cutting down is necessary to meet the needs of contour size, the yarn cutting down should be distributed uniformly in the whole composite material,and the number of yarn cutting down in every section should be no more than 10% of the total.