Seismic response of a new type of foundation，the composite caisson-piles foundation，is studied through a simplified analytical method. The focus is the contribution of the piles beneath the caisson in increasing the earthquake resistance of the foundation-superstructure system. Firstly，considering the interaction between the soil and foundation with dynamic Winkler model，the equation of kinematic response of the composite foundation under S-wave is derived. Secondly，a simplified model for the seismic response of the foundation-column-lumped mass system in frequency domain is built；and with Fourier transformation this method is applied to transient seismic problems. Thirdly，with an example of soil-foundation-superstructure seismic behavior，this proposed method is validated by comparison against 3D dynamic FEM modeling，in which domain reduction method(DRM) is utilized. Lastly，the significance and mechanism of adding piles in improving the earthquake resistance of the foundation and superstructure are analyzed through examples in different soil conditions. Discovery in this study is that adding piles under the caisson is an efficient way to increase the seismic resistant capability of the soil-foundation-superstructure system；and the main mechanism is the elimination of the pseudo-resonance.