Abstract: The internal defects formed in TC4 specimen manufactured by selective laser melting were determined by employing radiographic testing with their sizes quantitatively evaluated. With the computed radiography (CR), the radiographic detection sensitivity and minimum defect detectability of the artifical defects such as porosity amd poor fusion in TC4 specimen were studied. It is employed computed tomography (CT) to quantitatively analyze the defect sizes, corresponding three-dimensional morphology and spatial distribution. Comparing the detection difference between the two imaging methods reaches the following results. The CR test method can detect the simulated pore of ϕ0.4 mm and fusion defects with ϕ0.8 mm×0.3 mm in size. The CT method demonstrates higher detection sensitivity, which is suitable for defect detection, size evaluation and quantitative analysis of tiny pores such as the simulated pores of ϕ0.3 mm. The deviation between the sizes of artificial defect and actual object is within 10%. Moreover, the actual three-dimensional shape of the printed defects becomes more irregular with increased defect size.