Abstract: This paper presents the results of an experimental study conducted on the mechanical property of the two-step rectangle 3D braided composites. The tests include tensile in the axis, flexure and compression in the axis. Thus, the reliable mechanical property data are obtained. On the basis of the character of the microstructure, this paper relates the influence of microstructural variables such as the kinds and sizes of braider yarns, the linear density ratios of axial to braider yarn and the pitch lengths on the mechanical properties of these composites from a macroscopical view. It shows that the axial yarns dominate the tension and compression properties in the axial direction. The strength and modulus of tension and compression in the axial direction increase with the pitch length and size of braider increasing.