The laser interferometer has become a standard instrument in measuring the positioning accuracy and resetting accuracy of PCB NC machine.Aiming at the measuring data instability about positioning and repositioning precision,the measurement principle of the laser interferometer was studied,the relationship between the measurement distance and the wavelength and pulse number was obtained.The environment module data in production field were measured,the total compensation of wavelength variation was 0.23 μm,so the deviation caused by wavelength variation was almost negligible compared with the actual error.The main reason for the instability of measurement accuracy was the deformation of X axis joining pole.The structure of the X axis joining pole was redesigned.The stability of the accuracy compensation and measurement was achieved.