Given the limitations in current cross-borehole Electrical Resistivity Tomography (ERT) technology, experimental studies for CO? geological storage monitoring—primarily focused on static simulations and lacking methods to simulate the dynamic processes of CO? migration and leakage—an experimental ERT testing system was established. The system comprises a transparent sample-chamber, a CO? injection control device, a uniform light source, an image acquisition system, a SYSCAL PRO high-density resistivity meter, and Res2DInv inversion software. A static-validation and dynamic-measurement experimental scheme was designed. In the static phase, circular rubber pieces were used to simulate CO? to verify the system's accuracy in identifying the central position and area of CO? accumulation zones. In the dynamic phase, coarse sand and fine sand (quartz sand) were employed to simulate the reservoir and caprock, respectively, enabling monitoring experiments of CO? migration and leakage. The results demonstrate that the cross-borehole ERT system can accurately capture the distribution extent, migration trajectory, and leakage pathway of CO?, confirming both the usability of the developed system and the feasibility of the proposed experimental scheme.