Abstract: According to the engineering characteristics that carbonaceous slate of Muzhailing tunnel Lanzhou- Chongqing railway contained in fracture water and s oftened into water, the authors carried out basic mechanical property tests of carbonaceous slate what included triaxial compression, Brazil and wedge shear tests under the dry and saturated states. The results showed that the peak strength, failure strain and the elastic modulus of carbonaceous slate was accrescent with confining pr essure increased before and after water flling, but PoissonDs ratio was decreased with confining pressure increased. Meanwhile, the dry sample口s strength and elastic modulus sensitivity towards the confining pressure exceed the saturated sample. The peak strength of saturated specimen was reduced compare with the dry rock, how ever the peak strain was improved. At the same time, the shear strength envelope was obtained based on the wedge shear tests before and after water flling. Water ha s a significant impact on strength and deformation characteristics of carbonaceous slate.