Abstract: An X-ray three-dimensional imaging system for GIS(gas insulated switchgear) was developed, including subsystems such as mechanical, motion control, data acquisition, image reconstruction, and three-dimensional image display. The system was used to detect the GIS of a power supply station, and the results showed that the overall accuracy of the system reached 200 μm, and the highest resolution of the actual output tomogram could reach 3 160 pixel×3 160 pixel.