Abstract: In order to explore the influencing factors of conversion rate for mechanical property of carbon fiber using winding process, NOL ring properties with three kinds of T800 grade carbon fibers were tested. The effects of winding tension on the mechanical properties of epoxy resin matrix composites and conversion rate of fiber were studied. Moreover, mechanical property and microstructure parameters of damaged fibers after winding process were measured. The results show that winding tension changes fiber content, porosity, tensile property and failure mode of NOL ring. Crystalline structure, completeness of graphite structure and micro-defect of carbon fiber were characterized by means of X-ray diffraction, Raman spectrum and small angle X-ray scattering. The results demonstrate that the microcrystalline structure parameters of the damaged fibers don't change significantly, so the tensile modulus of the damaged fibers decreases negligibly. Pore defect of the damaged fibers increases with increasing tension, resulting in the decreases of tensile strength for fiber and the composite. The conversion rate of imported fiber is higher than those of domestic fibers, and the damage of fiber is weaker under the same tension level.