Abstract: Based on the exact dynamic-stiffness matrix of soil layers and half-space, the dynamic response of the horizontal layered site due to inclined waves is resolved. The displacement, stress and strain of every layer can be calculated. Based on the equivalent linear method, the nonlinear seismic response analysis of soil sites due to inclined waves (SH, SV and P) is presented. The study shows that the peak acceleration of ground motion is significantly influenced by the incident angle. The PGA is unnecessarily the largest for the vertical incidence. There can be multi-peak of ground motion due to inclined waves. The average incident angle of the actual seismic waves is about 60°, basically in agreement with the angle for the PGA due to incident SV waves. The results based on the vertical incidence may be unsafe. The necessity of oblique incidence in nonlinear seismic response analysis is shown.