Abstract: In this paper, the line attenuation coefficient affected by material composition and density was analyzed, the quantitative NDT method of materials density and the line attenuation coefficient comparison method based on materials composition by industrial X-ray computed tomography was described. As examples, the test method for X-ray CT systems equivalent energy measurement for some homogeneous aluminum alloy standard samples was studied, and the correlation of the CT value and the line attenuation coefficient at the equivalent energy was presented. With the help of the line attenuation coefficient and mass attenuation coefficient, the aluminum alloy materials densities could be determined. The experiment results showed that the measurement accuracy of density with the line attenuation coefficient comparison method based on materials composition characteristics was obviously better than density comparing method.