Abstract: The model of CT measurement for X-ray attenuation in metallic materials was established by using image Point Spread function(PSF) approximation, the numerical calculation on the gray scale amplitude perpendicular to the X-ray plane boundary was conducted by the measurement model, and the PSF curve was drawn. On this basis, the defects' quantitative evaluation model was presented according to the PSF curve for defects quantitative evaluation. The stainless steel sample containing artificial defects was analyzed by using the high-energy 6MeV industrial CT linear array detector system. The result shows that, compared with the traditional half-width defects measuring method, this method improves the accuracy of defects quantitative evaluation. This method provides a new and effective tool for high performance of quantitative evaluation on the defects in metallic materials.