A non-destructive method for detecting the screw motion precision of a machine tool relates to a machine tool precision detection technology, and the method has the steps as follows: (1) a basic working tool is arranged, an auxiliary working tool to be detected is arranged on a work bench of the machine tool; (2) debugging is carried out: a numerical controlled procedure of the machine tool is debugged according to data parameters of a standard thread, thereby allowing the screw motion of the machine tool to be coincided with the standard thread, the trial operation of the machine tool is started, and whether the screw operation of a main shaft of the machine tool is normal or not is judged; (3) a non-contact length meter is arranged: the non-contact length meter is arranged on a rotationangle adjusting frame, the light of a measuring head of the length meter is adjusted to be vertical to a tooth-shaped side surface of the standard thread; (4) measurement is carried out: the machine tool is started, and the screw motion precision of the machine tool can be measured. The method can intuitively non-destructively measure the tick values of the screw motion precision of the machine tool. The method is applicable to the machine tools of vertical machining centers, vertical milling machines, horizontal milling machines, lathes, turning centers and turning-milling complex centers, etc., which can carry out thread processing.