The invention provides a quantum key distribution phase decoding method and device and a corresponding system controlled by polarization phase difference. The method includes: an input light pulse isincident onto an interferometer including a beam splitter and a beam combiner to split the input light pulse into a first path and a second path of light pulses; first and second optical pulses are Transmitted along a first arm and a second arm of the interferometer, respectively, and are combined and outputted after a relative delay, wherein at least one of the input optical pulses or the firstand second optical pulses is phase-modulated; At least a first optical pulse is polarized into two polarizer optical pulses orthogonal to each other in polarization state, the two polarizer optical pulses are transmitted along two sub-optical paths, and then the two polarizer optical pulses are combined into a first optical pulse and transmitted to a beam combiner along a first arm; an integer multiple of the phase difference 2 pi between the two orthogonally polarized states of the input light pulse,which is transmitted through each of the first and second arms is controlled. The invention provides a phase coding quantum key distribution decoding scheme for resisting polarization-induced fading.