Abstract: It is important to know the factors affecting the displacements of excavation as to prevent failure of the excavation and optimize the design of the supports.In this paper an elasto plastic finite element method is employed to simulate the procedure of the failure of the supports for excavation,by which the factors are analyzed.The results indicated that the elastic modulus of soil and the supports has an effect on the displacements of the supports for excavation,but the modulus of the soil more serious than that of the supports.Based on the results,the deficiency of designing the supports by the conventional method and by elastic beam column method is discussed.In addition,the simulation shows no direct relation between the modulus of soil and the horizontal displacement on the top of the support.And then the conclusion can be drawn that monitoring the displacement of the supports for excavation by observing the displacement on the top of the support structure is not reliable.