The deformation behavior of the rock and soil is a key problem in the construction of the underground pipe work, and will directly influence the time limit and difficulty of a project. Actually for the underground rock mass, the construction of pipe work is a stress release process which makes the deformation characteristic of the rock mass totally different with other conventional constructions, such as building construction, road and bridge construction. The reason is the stress paths of the two kinds of engineering are different; one is download stress path and the other is upload stress path, so the mechanical property and deformation characteristic of a kind of soft rock under both download and upload stress paths in the Three Gorges area were studied by using the elastoplastic modeling method. Through the experiments of lamellar marlstone of Badong formation, the manner of the interaction between plastic volume stain and shear strain, the direct effect of the plastic volume stain on shear resistance were investigated, and the conclusion that stress path is exactly the comprehensive performance form of the interaction between plastic volume stain and shear strain which has been proved by the trixal experiments of soft rock. Finally, the deformation behavior of marlstone was used to calculate the settlement in the numerical simulation of the underground pipe work's construction.