The　earth　pressure　applied　on　the　lining　is　affected　significantly　by　the　soil　arching　effect　during　tunnel　excavation.　The　critical　depth　becomes　one　of　basic　parameters　to　determine　the　pressure　of　the　surrounding　rock　when　designing　the　tunnel　structure.　Based　on　the　additional　load　characteristics　of　the　surrounding　rock,　a　user-defined　elastic-plastic　material　subroutine　(UMAT)　of　the　constitutive　model　considering　complex　stress　path　of　soils　is　complied.　Three-dimensional　finite　element　analysis　of　tunnel　excavation　is　carried　out　by　means　of　the　secondarily-developed　ABAQUS　with　the　UMAT.　The　soil　arching　effect　is　studied　from　two　aspects:　the　deformation　law　of　the　surrounding　rock　and　the　stress　path.　According　to　the　results,　a　new　division　method　for　deep　and　shallow　tunnels　is　proposed,　which　can　be　illustrated　by　the　critical　depth.　The　critical　depth　is　determined　as　the　depth　in　accordance　with　the　vertical　displacement　of　ceiling　becoming　steady　when　there　is　no　supporting　structure,　and　the　depth　in　accordance　with　the　maximum　settlement　of　the　surface　soil　above　the　tunnel　when　supporting　structures　exist.　Compared　with　the　critical　depth　determined　by　the　code,　the　proposed　method　can　reflect　the　macroscopic　deformation　law　of　soils.　Moreover,　the　quantitative　impact　of　various　factors　is　taken　into　account　at　the　same　time.