A phase unwrapping method for phase-type optical fiber sensors and large-scale phase measurement is proposed, which combines the phase demodulation of 3×3 fiber coupler and the dual-wavelength phase measurement method in digital holography. The unwrapped phase of the synthesized wavelength is used to compensate the wrapped phase of the single wavelength. And the wide-range, error-free phase change information is obtained. The optical fiber Michelson interferometry system based on dual-wavelength of 1310 nm and 1550 nm is established. The large range vibration generated by the piezoelectric displacement platform is measured. And the feasibility and validity of this method are verified. Compared with the phase demodulated result of the 1310 nm single wavelength, the proposed method can make the measured optical path difference expand to 6.5 times.