Abstract: In order to investigate the damage evolution of 3-dimensional braided carbon-fiber reinforced SiC matrix composite (3D C/SiC) during fatigue and establish the model of relationship between variation rate of electrical resistance (ΔR/R₀) and fatigue cycles, tension-tension fatigue tests of 3D C/SiC were carried out under a maximum stress of 250, 255, 260 MPa, a sinusoidal loading frequency of 20 Hz, a stress ratio of 0.1. ΔR/R₀ was measured by electrical resistance appearance. The experimental results show that its ΔR/R₀ decreases at the first cycle and then monotonic increases with the increase of fatigue cycles, which mainly consist of steady increases, spurting and abrupt increases. Finally, based on the damage mechanics theory, ΔR/R₀ is selected as the fatigue damage variable, and the relationship between ΔR/R₀ and fatigue cycles was obtained, the modeling results have good agreement with the experimental results.