Abstract: The seismic response of underground pipelines is usually calculated by the wave theory that assumes seismic wave as a traveling wave, which propagates along the axial direction or at some angle with the axial direction. This method can only solve the axial force and strain of pipeline due to the phase difference of ground motion. Some reference documents assumed the earthquake ground motion as a stationary random process distributed in space and time, and worked out the seismic response of pipelines using random vibration theory. But they neglected the effect of non-stationary ground motion, and especially the non-stationary ground motion in time domain that may be the most important factor giving rise to the axial force and the strain of the pipeline. In this paper, the ground motion time histories of each spot in the pipeline axis are generated based on the statistical model of ground motion, and the seismic responses of the pipeline are worked out by the series method. The results may better reflect the non-stationarity of ground motion in time domain and are closer to reality than those by wave theory and stationary random vibration theory.