<p>Fault activation is a common phenomenon during coal seam mining in proximity to faults. To better understand the mechanism of roof water hazards caused by fault activation, numerical simulation was employed. By coupling FLAC3D with PFC3D, this simulation is mainly analyzed from four aspects: the number of contact forces, the evolution of vertical displacement, the development of the plastic zone, and vertical stress. Based on field test and numerical simulation, this study reveals that fault activation becomes more intense as the working face advances from the hanging wall to the footwall of the fault. In addition, fault activation exhibits distinct phases, each characterized by different mechanical behaviors. Furthermore, combined with the decreasing trend in the number of contact forces, the height of the water-conducting fracture zone shows a pattern of initial increase followed by subsequent decrease. These findings reveal that analyzing the mechanism of roof water hazards caused by fault activation provides a theoretical basis and valuable insights for preventing and controlling roof water hazards during coal mining operations near faults.</p>