The utility model discloses a three-point centring device for assembling a conducting rod, and the device comprises three supports which are uniformly distribute at a periphery. Each two adjacent supports are in detachable connection, thereby forming an annular frame through connection. A part, located at an outer side end of the annular frame, of each support is connected with a roller which is used for contacting with the inner wall of an installed tube body. The inner side ends of the supports are respectively connected with the conducting rod which is installed at the center of the installed tube body, and are respectively connected with a supporting plate for positioning the conducting rod. The supporting plates and the supports are connected with each other through an adjustable connecting mechanism which can adjust the axial position of the supporting plate. A side surface, contacting with the conducting rod, of at least one supporting plate is provided with an installation groove, and the interior of the groove is provided with a wedge which is used for the wedge-caulking of the conducting rod. The distances between two adjacent supporting plates can be adjusted, and the distances between the supporting plates and the support can be adjusted. The device is suitable for the assembly of installed tubes with different diameters and conducting rods with different diameters.