Abstract: The effects of the dynamic shear modulus ratio and the shear wave velocity on the surface ground motion and their equivalent effect relations with surface acceleration spectra are investigated by use of the numerical simulation method considering site types, incident seismic intensities and incident seismic wave forms. The results indicate that the errors of dynamic shear modulus ratio and the shear wave velocity both have strong effects on the surface ground motion. The effects of the dynamic shear modulus ratio and the shear wave velocity are more significant for strong nonlinear property in the weak site as well as for the cases when the two parameters by the tests are lower than the actual values, e.g., 6% error of the dynamic shear modulus ratio and 25% error of the shear wave velocity for 0.1g incidence in site Ⅲ can not be neglected. The effects of the dynamic shear modulus ratio alone and the shear wave velocity alone on the spectra can be expressed by the equivalent relationships for different site types, incident seismic intensities and incident seismic wave forms. The extent of the effects of the dynamic shear modulus ratio on the spectra is much larger than the shear wave velocity by 3⁵ times and the difference of the sensitive extent between the two parameters for the decreasing of the dynamic shear modulus ratio is more obvious than that of the cases for the increasing of the dynamic shear modulus ratio.