As a case study

based on a realistic tunnel

we use elastic-plastic method to calculate the deformation of tunnel after excavation.Using the three-dimensional fast Lagrange analysis of continua method we analyse the deformation of tunnel during excavation.The result shows that the critical depth of plastic yield is 78.2m.When the excavation reaches 31min the tunnel

the stress of surrounding rock is released and tends to stability.The maximum deformation of tunnel is at the sidewall during excavation.It reached 1.94mm.The deformation of surrounding rock tends to stability after excavation which holds some days.During the construction

the tunnel is in tensile failure state at the vault and bottom

but in shear failure state at the sidewall.The conclusion in this paper can be referred to the design of sandstone tunnel.