The utility model provides a vice automatic pretension device of two nut ball, includes giant magnetostrictive barrel, exciting coil, initial preloaded bolt and force transducer, giant magnetostrictive barrel suit is provided with force transducer between giant magnetostrictive barrel and the one nut on two nut ball accessory lead screws and at between the two nuts, set up initial preloaded bolt on the one nut, exciting coil arranges the outside of giant magnetostrictive barrel in through the coil former, is connected with between two nut ball accessory two nuts to prevent that two screw nut from taking place the double-screw bolt of relative rotation, exciting coil is connected with the controllable stable current source among the drive power supply, drive power supply includes microprocessor, D/A converter, controllable stable current source and self-correcting, and microprocessor is connected with D/A converter and self-correcting respectively, and the D/A converter is connected with the controllable stable current source, and the controllable stable current source is connected with exciting coil, and the self-correcting is connected with force transducer. The device safe and reliable has realized the automatic pretension of ball.