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Owing to the strong penetration ability of X-rays and the imaging visibility, X-ray inspection has been gradually applied to power grids. However, various problems occur in the promotion and application of X-ray inspection in ultra high voltage gas-insulated switchgear (UHV GIS) owing to its large size. These problems relate to parameter selection, photography, protection area, random defect recognition, and risk assessment based on the X-ray image. In this paper, an X-ray digital imaging system is set up for UHV GIS inspection. Parameter selection for UHV GIS is discussed, and we demonstrate that UHV GIS can be photographed under a source-to-detector distance (SDD) of 2.8 m, a tube voltage of 300 kV, and an exposure of >240 mA·s. A photographic method for UHV GIS, entailing adjustment of the position of the imaging plate with a fixed position of the X-ray generator, is proposed to reduce the difficulty in image stitching. The influence of the parameters on imaging quality is discussed, and we show that the brightness and contrast increase with increasing exposure or decreasing SDD. The interactions between parameters are qualitatively introduced. Moreover, the sensitivity of X-ray inspection in UHV GIS is studied under selected parameters, and the sensitivity of X-ray inspection to copper particles and aluminum particles in UHV GIS are shown to be <0.7 mm and <1.1 mm, respectively. Radiation protection for operators is also discussed. In addition, a pseudo-color scheme for identifying random tiny defects is proposed to reduce human error. Finally, the risk level of defects with X-ray inspection is defined by size feature. [ABSTRACT FROM AUTHOR]