Abstract: A pinhole is one of the key components in a phase-shifting point diffraction interferometer(PS-PDI).In order to study the effect of the size of pinhole,material of pinhole and thickness of material on the quality of diffraction wave-front,and determine the measurement accuracy of the PS-PDI,near-field data was obtained by means of the finite-difference time-domain method,and then the data of far field based on Rayleigh-Sommerfeld vector diffraction theory could be acquired from near field data.The quality of diffractive wave-front was analyzed under the uniform incident light with TE and TM polarization,and the corresponding curve was achieved.The results show that in order to obtain perfect wave-front,the thickness of material should not be less than 300nm.Appropriate aperture size can reduce the error of wave-front.When the size of pinhole is 300nm,the root mean square wave-front error is below λ/1000(λ=632.8nm).It is of great help to design and application of a PS-PDI.