Abstract: The seepage characteristics of rock joints and fractures are of significant importance for exploring the mechanisms of geological disasters induced by tunnel excavation. This study employs COMSOL numerical simulation software to investigate the cyclic water injection in rock joint fractures under varying amplitudes and frequencies. The results indicate that under cyclic water injection conditions, the flow pattern of the fluid within the fractures exhibits periodic changes with the inlet flow rate. Higher water injection amplitudes lead to more chaotic vortex patterns in low flow velocity regions. The permeability of the fractures also changes periodically with the inlet flow rate; specifically, when the injection flow rate decreases from its peak to its trough, the permeability increases from a trough value of 8.9×10?? m2 to 11.1×10?? m2. Moreover, the amplitude of permeability fluctuations increases with the rise in injection frequency and amplitude. Additionally, a simple and effective method for delineating flow regions is proposed, which allows for the identification and quantitative calculation of the main flow domain and vortex regions in the fractures.