Abstract: By computerized tomography(CT) technology, the inner close-grained degree of carbon/carbon(C/C) composties could be illustrated. Furthermore, according to the CT value given from the CT images, the density of the coposites could be calculated. Compare with the other methods for testing the density of the composites, the method has a higher precision and no need for more tested samples taken from the tested，thus the material can be saved. Moreover the method can also be used for testing the density of other porous composites besides C/C composites.