Abstract: 2.5D woven composites are resistant to delamination and impact, which have great application prospects in aeroengine structures. The first-order bending vibration fatigue tests under different stress levels were carried out for the specimens made of 2.5D woven carbon fiber reinforced bismaleimide resin matrix composites in the warp direction and weft direction, respectively. The experimental results show that the vibration fatigue performance of the warp specimens is better than that of the weft specimens. With the increase of stress levels, the lives of the specimens are shortened obviously, and the decline percentage of natural frequency increase, and the damage degree and damage propagation speed within specimens also increase. In the process of vibration fatigue test, the main failure mode of 2.5D woven composites was the loss of structural integrity caused by the debonding of the yarns and the matrixes, which leaded to the continuous decrease of the stiffness of the specimens. 3D CT reconstruction images of the internal damage of the specimens show that the damages spread throughout in the working section of the specimens. The higher the stress levels are, the greater the internal damage ranges and the higher the damage degrees are. And the internal damage state of the warp specimens is more serious than that of the weft specimens. The mathematical model of stress-life (S-N) curve of vibration fatigue of 2.5D woven composites is obtained by data fitting for vibration fatigue results under different nominal stress levels by using the log-log-linear life model, which can be used to predict the life of 2.5D woven composites.