The invention discloses an optical heterogeneity measurement device and method based on a dual wavelength fizeau interferometer. With the dual wavelength fizeau interferometer, interferograms of a reference light wave and a light wave reflected by the front surface of a to-be-tested flat mirror are sequentially collected, and wavefront aberration data [delta]W11(x,y) and [delta]W21(x,y) corresponding to wavelengths [Lambda]1 and [Lambda]2 are obtained by first phase shift measurement; interferograms of the reference light wave and a light wave passing through the to-be-tested flat mirror and reflected by the rear surface of the to-be-tested flat mirror are collected, and wavefront aberration data [delta]W12(x,y) and [delta]W22(x,y) corresponding to the wavelengths [Lambda]1 and [Lambda]2 are obtained by phase shift measurement; and a difference value is calculated by the wavefront aberration data corresponding to the wavelengths obtained by two-stepped measurement, and the optical heterogeneity of the to-be-tested flat mirror is obtained. The invention does not require a standard reflector, and completely eliminates influences of the surface shape of the standard reflector on measurement results. The measurement steps are simple, and the defects that the traditional absolute measurement method has tedious steps and is vulnerable to air disturbance are tackled.