The fiber Mach-Zehnder interferometer was used to produce linearly polarized Gaussian beams．A general expression for the light intensity distribution is derived for interference of two Gaussian beams and the fringe contrast is studied．The fringe contrast varies with the amplitude of Gaussian beams and the angle in between the polarization planes of two linearly polarized light． The theoretical description is validated by experiment．A formula for calculating the fringe contrast，which is shown to be in good agreement with the experiment results，is obtained． The research shows that the smaller the amplitude difference between two

Gaussian beams，or the smaller the angle between the polarization vectors of the Gaussian beams，the larger the fringe contrast．