The basic principle of polarization switching to eliminate polarization- induced fading in fiber optic interferometers is studied. A theoretical model is constructed and the complex method of complex is introduced to solve the problem that four signals compose one signal. Theoretical analysis and simulation show that polarization switching can eliminate polarization-induced fading. An experimental system based on non-balanced Michelson interferometer is built. Using phase generation carrier (PGC) modulation technology to demodulate signal, the antipolarization effect of the four-way polarization switching is tested by experiment. The results show that the birefrigent effect of the lead fiber can be eliminated after the signal is composed. After four signals compose one signal in the experiment, its visibility can be a stable level of 0.838. The result keeps with the visibility of Michelson interferometer under ideal condition, which proves the feasibility of polarization switching in elimination of polarization-induced fading.