The invention discloses a modulation and demodulation method and device for an optical fiber grating sensor based on phase shift signal modulation. The modulation and demodulation device comprises a laser source, an isolator, an optical switch, a phase modulator, a circulator, an optical fiber grating group, a signal generator, a photoelectric converter, a data acquisition module and a data processing module, and is characterized in that the laser source is modulated by using the optical switch so as to generate a pulse beam, then high-speed pulse phase modulation is performed on the pulse beam by using the phase modulator, the pulse beam is interfered in the circulator, multipath phase shift signals are generated and outputted via a third port, and vibration phase demodulation for an optical fiber sensor is realized by being cooperated with a demodulation method of a multipath phase shift algorithm. The modulation and demodulation method is simple in optical path, capable of forming a plurality of sensing modules conveniently, low in modulation requirement, simple in demodulation circuit, high in real-time performance and precision, wide in dynamic range and high in environmental interference resisting ability.