The polarization-coupling distribution in fiber coil and beat length of used fiber are achieved by testing polarization-maintaining fiber coils using white light interferometry. The polarization-coupling distribution of the fiber coil is obtained through this test, which is helpful in identifying the principal external factors affecting the polarization-maintaining ability of the fiber coil. By identifying the polarization-coupling peak produced by the two fusion splice points at both ends of the fiber coil and the white light interferometer, the optical path difference of the optical signal transmitted by the two orthogonal polarization axes of the fiber coil is obtained, and the beat length of the fiber coil is calculated. The experiment shows that the angle error can be recognized effectively when the angle is 0.13°. The results show that the polarization-coupling distribution and beat length of the fiber coil can be measured simultaneously using a white light interferometer, providing a simple and effective method for characterizing the polarization characteristics of the polarization-maintaining fiber coil.