Abstract: The dynamic triaxial tests on the unsaturated loess in Xiji region of Ningxia under different water contents are carried out. Based on the analysis of the influences of water content on the dynamic characteristics of loess, the influences of water content of soil on the surface motion intensity and characteristics of a loess sites are studied by using the method of soil seismic response analysis. The results show that with the increase of water content, the dynamic shear modulus decreases and the damping ratio increases. When the water content reaches the plastic limit, the influences of change of water content are obviously reduced. On the whole, with the increase of input seismic motion and the increase of water content, the PGA and the values of reaction spectral in the loess site increase. And the influences of water content on the ground motion intensity and characteristics are different in different sites. For the thinner site, when the water content reaches 20%, and the input seismic motion is greater than 50 gal, the magnification begins to decrease, and with the increase of the input seismic motion, the decrease amplitude increases, while the value of the long period component of the reaction spectrum increases, and when the input seismic motion of thicker covering site reaches 300 gal, the magnification decreases when the water content reaches 20%, but the value of reaction spectra increased obviously after 0.3 s.