Abstract: In view of the unique and complex microstructure characteristics of 3D fabric reinforced ceramic matrix composites, they face multiple severe challenges in predicting their service life under high-temperature thermal cycling when they are used as thermal protection materials. In this paper, the microscopic damage and mechanical properties of composites under 1200°C thermal cycling are studied by using a multi-scale model, combined with simulation analysis and experimental tests. The constructed multi-scale model describes the weaving of warp and weft, the geometry of the fibers, and the pore distribution in the matrix. The material constitutive used covers the yield phase of the matrix and takes into account temperature-dependent cyclic hardening effects. The simulation and experimental results show that the matrix cracking and interface debonding caused by thermal cycling are the main causes of microscopic damage, which greatly reduces the tensile properties of the composites. In contrast, bending and compression properties are less affected by thermal cycling.