<p>A novel real-time visual monitoring system was developed for observation of rock-joint deformation within a triaxial pressure vessel under high-pressure conditions. The system uses a small webcam housed inside the pressure vessel, able to withstand pressures of up to 20 MPa and connected to an external computer for real-time monitoring. The compact design ensures space efficiency and durability. Integrated with Digital Image Correlation (DIC) techniques, the system captures detailed displacement distributions during deformation processes. The system was applied in direct shear tests using a true triaxial apparatus to investigate the sliding behavior of rock joints, thereby elucidating the effects of joint roughness and pore pressure on the sliding process, as well as progressive changes in asperity geometry. The real-time visual observations, combined with quantitative DIC data, provide critical insights into the progressive deformation of rock joints, enhancing our understanding of subsurface geomechanical behavior.</p>