Abstract: A field monitoring programme is carried out for the open-excavated project of a subway station in Beijing,the trends of the displacements and the inner forces are under control,and the change of characteristics of displacements and inner forces in the retaining structure during the construction is analyzed.The necessary engineering measurements are taken to keep the stability of the excavated foundation pit.There are several monitoring conclusions as follows:a)the horizontal displacements of retaining structure increase with the construction duration and tend to be ltable gradually after the foundation-pit excavation is completed,The largest displacement appears on the second layer steel support tube and the displacement is the smallest in the bottom of retaining structure;b)the axial forces on the first layer steel-support tube significantly greater than those of the second and the third layers;and c)the axial forces on the diagonal steel-support tubes in the outside corner of the foundation-pit are much greater than those of the others.