The advantages and disadvantages of one- and two-beam polarization second-harmonic generation (SHG) techniques are reported for the determination of the second-order nonlinear effect of isotropic nanogold film. The results indicate that 100 nm gold film fabricated by radio frequency magnetron sputtering on glass substrates is isotropic in the plane of the substrate. Expansion coefficients for nanogold film in one-beam chiral experimental setup are not unique for the measurement of p-polarized initial beam and p±s-polarized secondharmonic beam, and they are unique for s- or (p + s)- polarized initial beam; but the uniqueness of expansion coefficients in two-beam geometry is without the limitation of the initial beam polarizations. The obtained results also show that one-beam technique only determines these contributions related to the effective electric-dipolar effect arising from the broken symmetry at the surface of an isotropic gold film, but bulk multipolar (magnetic dipole and electric quadruple effects) contributions of nanogold can be completely separated from its surface second-order nonlinear optical response in the two-beam setup, and all the non-vanishing tensor components obtained in both experimental geometries are very close in value and phase, and when only considering the surface electric-dipole effect of nanogold, the quality of its tensor components can also be checked by two-beam technique. So two-beam technique has more advantages than one-beam technique in the characterization of the nonlinearity of nanogold, and this conclusion can be applied to thin films /bulk materials with high structural symmetry.