Abstract: Three dimensional imaging of C/C composites was performed using micro-CT, microstructure defects such as voids, crack and inclusions were observed through the CT images. Three dimensional segmentation and extraction of voids, crack and inclusions were realized respectively by threshold segmentation etc, and the location and quantitative analysis were performed. Statistical analysis results show that there are 15261 voids and 25 inclusions in measurement volume. The average diameter size of void is 0. 41 millimeters, about 73. 25% void diameters are less than 0. 41 millimeters, and most of voids shapes are spherical or near spherical, the volume porosity of the specimen is 7. 56%. The structure characteristics of C/C composites were reconstructed by high resolution micro-CT, and the characteristics of the internal microstructure were extracted and statistical quantitative analysis were performed.