Abstract: Screw drive system is one of key parts of CNC machine tools, aiming at two bearing types of screw drive system as following: The first type that the screw system is bearing on one direction in both end, the second type that the screw system is bearing on one direction in one end and two direction in another end, through the analysis and authentication, it is pointed out that there are some shortcomings and defects in current conclusion as following about calculation and determination of preload stretching force of screw system: the preload stretching force be only taken into account in axial force is too large in general, and it is not given the calculation and confirmation methods considering overall the major factors of axial force and thermal deformation, or only take into account thermal deformation as calculate preload stretching force, so that the results is limited, unreasonable, imperfect. For overcoming these shortcomings and defects mentioned above, considering overall two main influenced factors mentioned above, the stress and deformation of screw system fixed both end are analyzed, a new technology parameter—critical preload stretching force is led-in, the equations and the solving method about comprehensive critical preload stretching force are inferred; the minimum load about bearing is taken into account, and the revise ratio are put in through taking into account practice conditions further, the representation about finally preload stretching force is produced; the selected principles and reasons about the revise ratio are discussed as well, so that the methods of calculation and confirmation about preload stretching force are clear, reasonable, corresponding to reality. The rationality of calculation method of preload stretching force is verified by experiment also.

Key words: calculation, preload stretching force, screw system