In this paper, a novel experimental equipment was developed to conduct stretch bending and compression bending load on rubber/cord composites, and its damage mechanism was studied. Macroscopic analysis revealed that the application of compression bending loads significantly accelerates the degradation of bending stiffness in the specimens. Microscopic characterization demonstrated the formation of numerous micro gaps between fibers during cyclic loading, with their population density being markedly increased under compression bending conditions. Through finite element analysis at the microscopic scale, these micro gaps were identified as stress-induced defects resulting from plastic strain accumulation in cord fibers. These defects, termed as "acquired defects", were found to exacerbate the stress state within the micro structure, serving as the primary initiation sites for composite damage. Based on the study of the damage initiation mechanism, a quantitative methodology was established to correlate fiber plastic strains with the dimensions of these acquired defects, enabling the prediction of defect size and their impact on the composite's stress state. This approach provides valuable insights for micro structure optimization and material performance enhancement in rubber/cord composite systems.