Abstract: With the development of digital technology, various types of digital radiography technology have been applied in industrial testing. In order to integrally understand and know about various types of radiography testing system for NDT persons, and rationally choose of radiography testing system according to the correlative feature and imaging mechanism for different objects, different applications and other specific conditions, this paper makes the classification and induction for current radiography testing systems: systems are classified into analog imaging and digital imaging according to the imaging techniques; and are classified into static imaging and dynamic imaging according to moving state of detected objects. Finally, the paper overviews the components, principles of digital radiography system, and its characteristics compared with the photographic film, and outlines imaging technology categories.