Abstract: By using the test data, the uncertainty of the dynamic modular ratio G/Gmax and damping ratio versus dynamic shear strain for the conventional soils in China is studied. The characteristics of the uncertainty distribution, the probability indexes as well as the range of G/Gmax and for the typical strains under different probabilities are presented. Based on 588 groups of test results from 42 cities and districts in 17 provinces in China, the uncertainty of the modular ratio and damping ratio versus 8 typical shear strains is analyzed. The results indicate that most of the uncertainty distribution of G/Gmax and is abnormal and that the statistic indexes for the probability are regular. The standard deviation and the variation coefficient of G/Gmax and are both significant, and meanwhile the maximum of the standard deviation just appears in the sensitive range for the seismic analysis of soil layers. The 95% reference values of G/Gmax and are quite different from the envelopes of G/Gmax and λ for all types of soils. The variation coefficients of G/Gmax increase with the increase of the shear strain, but the variation coefficients of decrease with the increase of the shear strain. The uncertainty of G/Gmax is obvious at the large strain, while that of is obvious at the small strain. The variation coefficients of are larger than those of G/Gmax, indicating the uncertainty of the dynamic damping is more remarkable than the dynamic modulus.