Abstract: Considering the importance of the maximum dynamic shear modulus of saturated clay soils in calculation, lab and in-situ tests are performed. According to the 463 tests finished in the past several years, the values of the dynamic shear modulus of the same soil are different in the lab and in-situ tests. The results obtained from the lab tests are mostly less than those from the in-situ tests, and the differences become greater with the increase of depth. Based on the relationships of the maximum dynamic shear modulus in lab tests with the depth, which follows the exponential function, the statistical formula of the maximum dynamic shear modulus in lab tests and the shear wave velocity in in-situ tests are obtained. Finally, the maximum shear modulus Gmax derived from the above formula is applied in the case of ground seismic response computation, in which Gmax obtained from the in-situ tests is also used. The results show that the statistical formula is reasonable and practicable, and the differences of the maximum shear moduli obtained in different ways will have great effects on the peak ground acceleration and the characteristic period of the seismic response spectra.