Pinhole is a key component in phase-shifting point diffraction interferometer (PS-PDI), therefore the production precision of pinhole will seriously affect the detection accuracy of interferometer. For most of the diffraction problems, the theory of scalar diffraction is a good approximation. However, the theory of vector diffraction is more suitable to explain the actual situation of diffraction wave surface when the diffraction aperture is very small. On the basis of the scalar and vector diffraction theory, effects on the quality of diffraction wave-front produced by the size of pinhole are analyzed, in the meantime, the peak and valley (PV) value and root mean square (RMS) value of diffraction wave front errors are calculated while visible lights entranced the pinhole. The results show that with the scalar diffraction theory, when aperture is 400 nm, RMS of diffraction wave front error is the minimum and changes little with the material thickness. As well, with the vector diffraction theory, when aperture is 200 nm, RMS of diffraction wave front error is the minimum, but it changes greatly with the material thickness.