The quality of the reference wavefront is constrained by the diameter of pinhole, which is the critical element that determines the precision of phase-shifting point diffraction interferometer (PS/PDI). The effects of film thickness, diameter of the pinhole, machining error and single and multiple aberrations of incident light on the diffraction wavefront errors are analyzed based on the vector diffraction theory. The analysis shows that in order to obtain a reference wavefront with a numerical aperture of 0.2 and a root-mean-square (RMS) wavefront error below 1.4×10-3λ, the best choice for the pinhole is the material chromium with a thickness of 200 nm and diameter of 1.5 μm, and the simulation error requirements should be satisfied in machining. The test window size is optimized based on the spatial frequency domain analysis. The results reveal that the optimal window size is approximately 60 μm. Experiments are carried out for the designed mask to verify the feasibility.