Based on interference principle of equal inclination. The distribution of intensity,visibility and fringes were analysed theoretically,and the influence of incidence angle on the distribution of intensity and visibility and of phase angle on the distribution of fringes by medium film reflection for a Gaussian beam discussed. Numerical calculation results show,on a plane vertical to the direction of light propagation,it is a circular spot for reflected light in the region of super-position. With the increase of incidence angle,the visibility reduced gradually,the reflected intensity deviated from Gaussian distribution,the size of beam spot broadened,the peak value reduced. The distribution of fringes by medium film reflection for a Gaussian beam in space is similar to that of a plane light,which is mainly decided by incidence angle and thickness of medium film.