Following problems are discussed in this report: 1) It is proved by analysis that the regulation sensitivity of sandwioh holography is much lower than that of double plate holography. 2) The dependence of regulation sensitivity on the parameters of optical path are given. 3) For reference plane wave, it is proved that there is no distortion of image as certain approximate conditions are satisfied. 4) It is indicated that both sandwich and double plate holography have inherent defect of additional error because of the optical inhomogeneities in the substrate of the holographic plates.