When a Hartmann-Shack(HS) wavefront tester is used to test lenses with high numerical apertures, the spherical reference wavefront from nanometer pinholes should be taken to calibrate the H-S sensor. To fabricate a high quality pinhole, this paper analyzes the factors affecting the quality of reference wavefront to obtain the optimal parameters of the pinhole. The vector diffraction of the pinhole is calculated based on the vector diffraction theory, the effect of the thickness, diameter of the pinhole on the diffraction wavefront errors is analyzed and the aberration, power transmission, intensity uniformity, fabrication errors and incident light with shift, defocus and tilt are discussed under a converging Gaussian incident light. The calculation and analysis show that in order to obtain a reference wavefront with a numerical aperture 0.6 and a peak-to-valley(P-V) value below 0.005λ(λ=193 nm), the best choice for the pinhole is the material chromium with a thickness of 200 nm and a pinhole diameter of 180 nm.