The utility model discloses a flash X-ray apparatus diode centering tool. An anode rod seat, used for mounting an anode tungsten pin, of a diode is conical, a through hole is formed in the center of the anode rod seat in the axial direction, the outer wall of the anode tungsten pin mounting position fractures in the axial direction, and threads are arranged on the outer wall. A tool body used for mounting a cathode ring is a T-shaped column, a tool body used for centering the anode tungsten pin is a cylindrical tool body, the outer surfaces of the tool bodies are made of stainless steel, the interiors of the tool bodies are made of organic glass, and a through hole is formed in the center of the column along the axis. A connecting block is arranged on the outer side circumference of a shielding cover plate, and the connecting block is connected with a shell through a screw. By using the tool, the integrity of the anode tungsten pin can be guaranteed, both the front side and the back side of the anode tungsten pin can be used, and cost is saved; the anode tungsten pin and the cathode ring can be centered fast by one person, adjustment time is saved, and working efficiency is improved.