Abstract: Detecting with γ-ray scanning is a new advanced technology of overhaul and maintenance. With the character of γ-ray damping in substance, it can detect and distinguish condition inside the equipment and provide evidence for monitoring equipment operation and overhaul and maintenance of the equipment. The basic principle and technical characteristic of the technology and its application condition in vacuum towers were introduced simply. The result of detecting application indicated that γ-ray scanning can detect and evaluate corrosive condition of packing layer in vacuum tower，and can also provide evidence for the adjustment on operation or overhaul and maintenance of vacuum tower. It possessed good extension and application value in petroleum and chemical industry，and so on.