Abstract: The vibration properties of 3D four-step rectangular cross-sectional braided composites cantilever beam with experimental verification were studied. Based on the meso-structure and unit cell model of four-directional and five-directional composites, the law of vibration characteristics influenced by material parameters (i.e. braiding angle and fiber volume fraction) was explored by the theoretical analysis. By analyzing and modifying the three-cell model, the first order natural frequency was obtained from global stiffness using the rule of mixture method, while loss factor was obtained by calculating the consumed energy by yarns with different orientations and matrix, and the whole vibration energy in a vibration cycle. Comparing the calculation results with the experimental results, the first order natural frequency increases with fiber volume fraction, but decreases with braiding angle; while loss factor increases non-linearly with braiding angle, but decreases with fiber volume fraction.