On the basis of Cam-clay Model, a proposal constitutive model on porous elasto-plastic geo-material was derived for the argillaceous shale, which was porous and easy to decompose with water, and then the mechanical behavior in an argillaceous shale tunnel was simulated. According to the mix theory, the argillaceous shale was analyzed as a three-phase mixture coupling with solid-liquid-air, and the effective stress was introduced to set up a proposal constitutive model. The constitutive laws relate: the evolution of the constitutive effective stress with imposed solid matrix deformation, the degree of saturation with suction stress, and the relative flow vector with intrinsic pressure for the water and air phases. Based on the FORTRAN language, a Finite Element Method program was coded, with a material subroutine named POROSTONE for the argillaceous shale elasto-plastic model, and then a soft argillaceous shale tunnel was simulated. At last, a compared analysis was derived with the data in-situ. Some results are revealed as follows: the porous elasto-plastic model works well and are in good agreement with the measured data in-situ; the deformation velocity is fast during the prophase of the tunnel excavating, compared with the later, but the steady time is long; some assistant measures, especially the lock-foot anchor should be set to enhance the steady state due