Abstract: Optical fiber interference spectrometer is widely used in various fields of substance detection, because it has many characteristics such as small size, high resolution, anti-electromagnetic interference, high temperature resistance, etc. A spectrum measuring system based on Mach-Zehnder optical fiber interferometer is designed, which uses an electric optical fiber delay line to modulate the optical path difference.System constitution is introduced, spectrum calculation formula and spectral resolution calculation formula are deduced.Then experimental platform is setup, and a light source with wide spectrum is measured by the system, interference signal is collected and its spectrogram is demodulated.Results show the spectral resolution is 2.085 4 cm^-1, when the maximum optical path difference is 0.479 5 cm. Analysis on the system shows that, performance of the optical fiber delay line, to a great extent, determines the resolution, accuracy and precision of the final demodulation spectrum, especially the accuracy of the speed and the delay time, and the linearity.