Abstract: This paper calculates the elasto-plastic problem of elliptical tunnelwith perturbation methods. It is supposed that material is ideally elasto-plastic according with Coulomb yielding critcrion and an annular region around tunnel has entered plastic yield. This paper gives analytical expressions of the stress, and elasco-plastic interface when second step small amount is concerned. In last examples, mechanical characteristic of the plastic region form and tunnel form isdiscusscd ualitatively and quantitatively.