Based on the polarization effect of metal-dielectric reflector in the point-diffraction interferometer for high-precision spherical surface testing, the oblique-reflection wavefront aberration of beams with different polarizaed states at various aperture angles is analyzed in detail. According to the numerical simulation result, the characteristic of oblique-reflection phase shift introduced by metal-dielectric reflector is studied, based on which the corresponding calibration method is presented. The experimental validation with the point-diffraction interferometer for high-precision spherical surface testing is carried out. Experimental results indicate that the metal-dielectric reflector introduces various effects on the beams with different polarized states, and the oblique-reflection wavefront aberration can be calibrated by the proposed method, with the residual error peak-valley (PV) value dropping from 0.0452λ to 0.0194λ and root mean square (RMS) value from 0.0075λ to 0.0021λ (λ is wavelength).