The invention discloses an assembly fixture for three-phase common-box conducting rods. The assembly fixture for the three-phase common-box conducting rods comprises a supporting frame, three supporting grooves used for supporting and locating the conducting rods are arranged in the supporting frame, the positions of the three supporting grooves respectively correspond to the mounting positions of the conducting rods in a mounted pipe, stopping structures used for stopping the conducting rods and preventing the conducting rods from separating from the supporting grooves are arranged above the notches of the three supporting grooves respectively, three supporting legs are arranged on the supporting frame, the three supporting legs are located in a circular plane perpendicular to the axes of the conducting rods and extend in the radial direction, the outer ends of the three supporting legs are connected with wheel frames through adjustable connecting mechanisms, and rolling wheels used for making contact with the inner wall of the mounted pipe are mounted on the wheel frames. The assembly fixture for the three-phase common-box conducting rods is light and handy in structure, convenient to use and capable of being applied to mounted pipes of different diameters, and using cost is lowered.