Abstract: The mechanical response of double row pile under step excavation is studied through numerical simulation and using general international geotechnical analytic software FLAC; and the working character istics of the double row pile retaining system are discussed according to the distance between two rows and the insertion depth of a pile.The study shows that the space effect of a portal frame will be poor if the distance between two rows, s4d (d is the diameter of the pile).When s 8d the space effect of the portal frame is also poor with a tie beam acting as a tie bar. The rational range of the distance between two rows is 4d～8d. The displacement of a pile is decreased and its internal force is increased with increasing the insertion depth of the pile.