Abstract: The underground pipeline in liquefaction soil under seismic force was simplified as a simple beam with elastic supports on two ends. Considering the interaction of buried pipeline-soil and fluid-structures, the mode superposition method was used to analyze the dynamic response under seismic loading of underground pipeline. The influence of the parameters of the pipeline, flowing fluid and liquefied soil on floatation response were under discussion. The numerical results show that the floatation displacement of the pipeline buried with soil liquefied under the action of seismic loading is proportional to pipe length and diameter, fluid flowrate inside pipeline, the density of liquefaction soil and axial sectional pressed force of pipe as well, but is proportional conversely to the fluid density inside pipeline, relative elastic coefficient of liquefaction soil, visco-elastic coefficient of pipe and the axial sectional drawn force. The effect of seismic acceleration amplitude on the floatation of pipeline is a trace that can be ignored in the floatation response analysis.