The invention discloses an external thermionic cathode distributed X-ray device. The X-ray device is provided with a vacuum box, multiple electron emission units, an anode and a power supply and control system, wherein the periphery of the vacuum box is sealed, the inside of the vacuum box is in a high vacuum state, the electron emission units are mutually independent and are arranged to form a linear array and installed on the side wall of the vacuum box, the anode is installed in the middle inside the vacuum box and is parallel to the arrangement lines of the electron emission units in the length direction, the anode and the installing plane for the electron emission units form a preset included angle in the width direction, and the power supply and control system is provided with a high-voltage power supply, a focusing power supply, an emission control device and a control system. Each electron emission unit is provided with a heating lamp filament, a cathode connected with the heating lamp filament, an insulation supporting part surrounding the cathode and the lamp filament, a focusing electrode located above the cathode and configured at the top end of the insulation supporting part and a connecting fixing part arranged above the focusing electrode and connected with the box wall of the vacuum box in a sealed mode, wherein a lamp filament lead penetrates through the insulation supporting part to be connected with the emission control device.