Abstract: To accelerate application of digital radiography(DR) in practice, the problem that how to evaluate the defects in corresponding digital images should be solved. The digital images acquired by DR system with linear array detector are likely to be magnified and distorted, thus make against defects evaluation. To solve the problems mentioned above, scale specimen for image evaluation was designed and applied in DR. It showed that with the help of scale specimen, defects evaluation can be achieved easily and accurately.