Abstract: The deterioration of the thin bedrock mining crack channel under the loose layer induces sudden water and sand inrush disasters, which seriously threatens the safe production of the mine. To investigate the spatiotemporal evolution characteristics of mining-induced fracture channels in overlying strata and the two-phase (water-sand) initiation-transport mechanisms within them, four types of transient models for fracture degradation were constructed based on numerical simulations of mining-induced thin bedrock beneath unconsolidated layers. By analyzing parameters including instantaneous fracture morphology (aperture and geometry), sand particle size, and hydraulic pressure conditions, key indicators such as sand inrush volume, mass flow rate, sand arch formation time, rise-span ratio, arch foot line angle, and contact stress distribution were systematically evaluated. This approach enabled the characterization of water-sand migration dynamics and arch-induced stagnation patterns within mining fractures, thereby revealing the alternating spatiotemporal catastrophe mechanism of water-sand transport-stagnation cycles during overburden fracture propagation. The spatiotemporal evolution of water-sand migration in mining-induced fractures of overlying strata is characterized by alternating phases of sand arch formation/stagnation and arch instability/flow inrush. The relative relationship between fracture aperture and sand particle size (termed “aperture-particle ratio”) is identified as the critical determinant of sand arch formation or instability. Both sand particle size and hydraulic pressure are found to exert dual-directional promotion effects on these processes. During the arch formation/stagnation phase, increased particle size and hydraulic pressure enhance arch formation probability and stability, thereby reducing disaster risks. Negative correlations are observed between particle size and arch particle count and between hydraulic pressure and arch formation time, while positive correlations exist with arch stability. Conversely, during the arch instability/flow inrush phase, sand inrush mass flow rate shows linear positive correlations with particle size and hydraulic pressure. Increased particle size and hydraulic pressure inversely amplify disaster risks. These findings reveal the alternating catastrophe mechanism of water-sand transport-stagnation cycles in mining fractures, providing theoretical insights for disaster prevention and control.