The principle of the mode coupling in polarization maintaining fiber (PMF) is analyzed. The measurement method of polarization coupling based on white-light interferometry with Michelson-interferometer is presented. The optical path difference (OPD) between the two arms of Michelson interferometer, changed by the movement of the scanning arm reflector driven by a step motor, compensates the OPD of the two orthogonal beams resulting from polarization coupling to realize the measurement of polarization coupling intensity and the spatial distribution along the PMF. Analysis and emulation are carried out for the disturbance signal of the mechanical scanning vibration and the influence of the vibration imposed on the output signal. The coupling intensity is calculated from the envelope of the output signal which is extracted by Hilbert transform and least squares Gaussian fitting under different scanning speeds. It′s indicated that the vibration amplitude and frequency which affect the detection accuracy are related to the scanning speed. And the detection error reaches the minimum when the scanning speed of the system is from 0.7 to 0.9 mm/s.