Abstract: In order to investigate the damage development regularity of composites subjected to fatigue loading, a normalized derivative damage model based on the residual strength was proposed. In this model, it is assumed that the cumulative damage and stress level have a linear relationship, based on which, the damage curves of untested stress levels can be derived from that of tested stress levels with positive stress ratios. Fatigue tests of 8mm-diameter carbon fiber reinforced polymer (CFRP) composite tendons for different stress situations were conducted, and the experimental data of glass fiber reinforced polymer (GFRP) composite laminates from references were adopted to validate the reliability of the proposed damage model. The experimental results show that the damage model can well reflect the three-stage development law of CFRP composite tendons, and the derived damage curves show a good agreement with the damage curves obtained by fitting the experimental data. Besides, this paper investigates the influence of stress level on the damage evolution of composites. As the stress level increases, the boundaries between adjacent stages of damage curves become unobvious.