When multi-layer thin film reflectors and beamsplitters are used in diffraction-limited imaging systems (such as a mask projection aligner) and in precise interferometers, where elements mentioned above are used in cone beams, special attention should be paid to the phase distortion and dispertion induced by these elements. Reflective phase distributions of some specific films are calculated by using the well-known characteristic matrix method. It is explicated that an element of this kind acts as as a phase distortion element with respect to the incident angle and as a phase dispersion element with respect to wavelength. For a 71-layor UV wideband reflector，the phase distortion and dispersion can reach 3; for a 31-layer neutral reflector, 0.78; for a 6-layer prism beamsplitter, 0.2. Moasuromont of phase distortions bj means of polarization holographic interferometry is described in details in this paper. Information about tho phase distortion of a whole wayefront can be obtained directly. At the end of this paper, it is pointed out that the experiruental results agree well with, numerical analysis.