Abstract: Abstract: In order to accurately measure the pulse equivalent and return difference of stepping motor, a laser micro-displacement measurement system is proposed based on thin film interference. The system includes He-Ne laser source, the Newton-ring device system, the planar CCD video signal gather system, the computer and data processing software. The measurement of micro-displacement is carried out by counting the fringe numbers with the resolution of 1/400 wavelength. The precision, sensitivity and stability in this system have been improved compared with traditional measurement technique, and the system is particularly suitable for the micron, sub-micron measuring range. The results of measurement with TSA50-C commercial stepping motor show that a displacement accuracy of nanometers scale is achieved in the common laboratorial environment. The results indicate the relative error for less than 5 m displacement of pulse equivalent and return difference. are 2.63% and 0.44% respectively.