Abstract: As a new X-ray inspecting technology, the digital radiography is seriously different from film radiography due to the difference between the digital detector and film. As a result, the image qualities of these technologies have more differences, especially in the influence factors and representation parameters. This paper analyzes the difference between digital radiography and film radiography, advances image quality evaluation parameters for digital radiography technology, i.e. contrast and resolution, and especially emphasizes importance of resolution for inspector to avoid undetected small defect by excessively heightening contrast and reducing resolution.