Abstract: Thermal expansion coefficient (TEC) is an important thermodynamic parameter of high-temperature resistant composites. The evolution behavior of the TEC of damaged 2D-C/SiC composites with ambient temperature was studied by theoretical model and experimental tests for the phenomenon of matrix cracking and interface debonding, which affects the thermal expansion deformation of the material under service condition. Firstly, the three-dimensional thermal mismatch stress calculation model of constituents was given based on minicomposite model. Secondly, matrix cracking and interface debonding were introduced, and the analytical expressions for axial and radial TECs of minicomposite were derived by considering thermal expansion difference between the fibers and matrix, transverse isotropy of fibers and the Poisson's effect. Thirdly, based on the 0/90 cross-ply laminate model and the macro-strain consistency assumption, a predictive model was established towards the apparent TEC of damaged 2D-C/SiC composites. Finally, the present model was compared with the classical Schapery model and experimental data, and the main influencing factors of TEC were analyzed. Parameter analysis indicate that the apparent TEC of the material is affected by matrix crack spacing, interface debonding ratio, porosity, elastic modulus and TEC of the constituents, among which the influence of the matrix expansion coefficient is particularly significant. The verification results show that the proposed model is reasonable and correct, and the predicted results are in good agreement with the classical model and experimental curve.