Abstract: X-ray voltage is one of the most important process parameters in digital radiography (DDA+CR). At present, domestic and foreign standards have given corresponding recommended values for the selection of the voltage during digital radiography, mainly considering that the higher tube voltage will reduce the primary contrast of the radiation detection. Comparison was made for the image quality and rate of defect recognition on changing X-ray voltage in DDA and CR, and then the reasons of the differences were analyzed. It was proposed that a higher X-ray voltage within reasonable limits and corresponding image processing technology could improve the signal-to-noise ratio of the digital image, and this would compensate for image sensitivity loss due to voltage increase, and ultimately improve the rate of defect recognition. The recommended value of the tube voltage based on the experience of the traditional film photographic process is not suitable for digital radiography. It is necessary to carry out relevant tests according to the specific detection system to determine the upper limit of the X-ray tube voltage, and the upper limit is much higher than recommended value by relevant standard.