Abstract: In view of the common delamination cracking in the preparation of C/SiC composite panel, the characteristics and properties of the products produced by resintransfer infiltration pyrolysis (RTIP) molding/densification process were analyzed. The observation of delamination morphology shows that the interlayer defects in the early stage of preparation and the late stage of composite have two different characteristics: delamination between carbon fiber bundles and internal cracking of carbon fiber bundles.Non-defective specimens of C/SiC and specimens with different interlaminar defect scales under different characteristics were cut and prepared, and the strength performance were tested. The mode-Ⅰ and mode-Ⅱ interlaminar fracture toughness tests did not produce the phenomenon and data characteristics of interlayer crack tip propagation, so it is inferred that the interlayer tip propagation resistance of these defect is obviously greater than that of machining cracks used in standard tests. Furthermore, in-plane tensile and in-plane compressive tests were carried out, and the mechanism of material properties attenuation was analyzed, and the law between the material properties and interlayer defect scales was obtained by fitting the experimental data. In order to represent the overall damage morphology of the specimen and the material details of the interlayer defect region, a multi-scale macro-meso integrated numerical modeling method was adopted, which is composed of meso-morphology structure near the defect, macro-equivalence in the distance and the gradual transition connection between the two regions. The characteristics of the calculated stress field further verify the rationality of the experimental analysis.