Abstract: During the forming process of composite components with complex-shaped geometries, the fiber preform would deform significantly in macro-scale. The bending performance of the preform has a decisive impact on the formation and evolution of wrinkle defects. The three-point bending method was employed to test the carbon fiber 3D woven preforms. Micro-scale deformation mechanisms of the preform were researched using the Micro-CT technology. Effects of structural parameters such as warp density and weft density on the bending property of the preforms were analyzed. It is shown that the critical bending energy of the preforms increases linearly with the increase of weaving point density. The macro-scale bending deformation of the preform is mainly composed of micro-scale deformations such as changing of warp yarn buckling degree, local compression buckling of warp yarns and slippage between warp and weft yarn layers.