Abstract: In order to find out defects affecting the thermophysical properties within the C/C composites, the artificial and natural defects in carbon felt-based C/C composites were detected by infrared imaging system equipment, which used the thermal conductivity characteristics of C/C composites. The study found that the defects inside the felt-based C/C composites could be detected by the reflection infrared imaging method and the detection capabilities was relevant to the thermophysical properties of composites. Larger artificial defects could be detected by infrared imaging in a greater depth, where as the smaller artificial defects could be detected by infrared imaging with reduced depth of defect.