Abstract: This paper presents a method of the displacement measurement using the technology of fiber Bragg gratings.After a broadband light source passes through separate Bragg grating,the synthesized light source,which a temperature stabilizer controls the stability of wavelengths,is obtained.The synthesized wavelength is longer than those of conventional light source,so the permitted measured range of path-length is enhanced by several hundred times.the measuring accuracy of the interferometer is improved because of the wavelength accuracy of fiber Bragg gratings.Inaddition,a M-Z interferometer used for high precision displacement measurement proves that this system with simple structure can complete the high-precision measurement.