In order to understand the stability and deformation mechanism of tunnel through fault zone,and to provide theoretical basis for scientific analysis of tunnel excavation through fault fracture zone, a large-scale direct shear test was carried out on the contact surface between the viscous mud-rock mass and the bedrock with joint surface,and the influence of normal pressure, stone content and rock dip angle on the interface mechanical properties of the viscous mud-bedrock contact surface was studied. The test results show that: The interfacial stress-strain relationship shows softening characteristics at low normal stress,and gradually transitions from weak softening to weak hardening with the increase of normal stress; The normal stress is positively correlated with the initial tangential modulus of the interface. The shear strength and stiffness of the interface increase with the increase of stone content; Compared with the block angle of 0°, the interface strength corresponding to the rock angle of 90° is improved; The internal friction angle of the interface has a linear positive correlation with the stone content, and the cohesion path has a negative correlation. When analyzing the stability and deformation mechanism of tunnel crossing fault zone, it is necessary to fully consider the influence of interface normal stress, stone content and rock inclination angle on interface strength.