Abstract: For any testing problem, the design of the testing technical classification is just the design of the testing image quality. The design of the testing image quality determines mainly the necessary achieve contrast and unsharpness of the image upon the expectant detective flaw. The contrast value can be designed on the established correlation in radiology between flaw imaging and IQI imaging. The unsharpness value must be designed on the sampling theorem. A practice designing procedure of testing technical classification was given for detection of gashole flaw.