Abstract: The ball screw pre-tensioning structure can solve the problem of thermal error, but the common pre-tensioning method causes the ball screw support bearing to bear a large axial force, which affects the service life of the bearing.Taking the X-axis ball screw of a certain type of CNC lathe as the research object.The unloading type ball screw pre-tension structure is designed to make the axial force generated by the pre-tension act on the thrust bearing.Tests have proved that this structure can not only improve the positioning accuracy of the machine tool, but also achieve the purpose of using the unloading the ball screw supporting bearing.