The dynamic shear modulus Gd and the damping ratio D are two main parameters in geomaterials seismic response analysis and the initial condition is one of the principal factors affecting the dynamic parameters. This paper studies the effects of initial stress ratio and moisture condition on dynamic shear modulus Gd and damping ratio D of loose deposit with large-scale dynamic triaxial tests. The experimental results show that the stress ratio Kc has important effect on the maximum dynamic shear modulus Gdmax of loose deposits. In a certain range of Kc=1-3

the stress ratio is larger

the maximum dynamic shear modulus is greater. Based on Hardin’s equation

an improved empirical equation considering the effect of stress ratio is proposed. By comparing the two Gd/Gdmax-?dn curves of saturated and air-dried loose deposits

the curve under air-dried condition is found to shows more obvious nonlinearity than the one under saturated condition. Moreover

the damping ratio under air-dried condition is slightly greater than the one under saturated condition. The proposed improved empirical equation of Gdmax and the nonlinear relationships of Gd/Gdmax-?dn are used to analyze the ground response spectrum of loose deposits. The calculation results show that the stress ratio and moisture condition influence the ground response spectrum obviously.