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In the present work, the microstructure deformation and synergetic damage evolution of a three-dimensional textile SiC/SiC ceramic-matrix composites under flexural loading, has been investigated by in situ digital image correlation at ambient temperatures. With the flexural loading increases, matrix cracking occurs on the tensile side initially, and the local stress concentration leads to matrix cracking, interlayer debonding and fiber breakage on the compressive side of materials. Different from traditional 2D braided composite, when matrix fracture occurs, a matrix crack propagates in matrix enrichment regions perpendicular to fiber tows, with local deflection near the fiber/matrix interface surfaces, its propagation is diffused into sinuous fractures, and finally present a H-shaped path feature. This processes dissipate strain energy, resulting in enhancing composites fracture toughness. By using continuum damage mechanics and thermodynamic framework with synergetic effects of microstructure, asymmetric tension and compression load on both sides of the material, the flexural loading-induced damage is characterized by the reduction of the macroscopic effective elastic modulus, and a synergetic damage evolution model is established, which reveals the relationship between energy release rate and elastic modulus degradation, and can be used to predict the flexural stress-strain curves of the 3D textile SiC/SiC composites, further to improve the design and assessment of new textile architecture with specific mechanical properties.