<p>Utilizing a model-testing system for karst tunnels, this study investigated the effects of cavity location and water pressure on the water pressure distribution behind the tunnel lining, surrounding rock pressure, and lining stress. Furthermore, the impact of cavity location and water pressure on the development of plastic zones in the surrounding rock of karst tunnels was determined, and the effect of the net distance between the cavity and the tunnel on structural stresses was revealed. Key findings indicate that: The presence of a cavity induces a distinctive “maple leaf” pattern in the Mises stress distribution on the tunnel lining section; When the water pressure in the karst cavity remains constant, the Mises stress at a specific monitoring point on the lining is most significantly affected when the cavity is located at the tunnel crown, with minimal impact when it is at the tunnel invert; Under water pressure, the deformation curve of the tunnel support structure exhibits a generally “concave” shape, with the indentation directed towards the cavity center. This phenomenon intensifies with increasing water pressure and higher relative cavity positions; The influence of water pressure on the lining axial force is complex, necessitating particular attention to the bearing capacity of the tunnel invert structure; The effect of hydraulic head on surrounding rock pressure follows a distinct pattern, and its analysis must account for the evolution of the rock mass structure under dynamic pore water pressure conditions.</p>