Abstract: To address the technical challenges of sparse monitoring points in the protective range and significant errors in determining protection boundaries during close-distance upper protective seam mining, this study takes the 21311 working face of Xiangshan Mine as the engineering background. By integrating FLAC^3D numerical simulation with field multi-borehole joint measurements, a systematic analysis was conducted on the spatiotemporal evolution of the stress field, plastic zone, expansion deformation, and permeability of the protected seam during upper protective seam mining. The effectiveness of gas control measures was also evaluated to achieve precise delineation of the pressure-relief range and optimization of the monitoring method. The results indicate that the floor stress field evolution exhibits a three-stage characteristic: “local pressure relief-symmetrical expansion-steady-state balance”. The maximum vertical stress reduction in the pressure-relief zone reached 95% of the original rock stress. The plastic zone expanded in a “trapezoidal” pattern, with a maximum failure depth stabilized at 30 m, ensuring the protected seam entered a fully fractured and pressure-relieved state. The expansion deformation rate and permeability showed a “saddle-shaped” symmetrical distribution, with the permeability in the core pressure-relief zone increasing to 172.5 times its original value, providing favorable channels for efficient gas drainage to optimize the field monitoring approach, 20 boreholes were strategically arranged along the strike (Group A at the open-off cut side and Group D at the final line side) and dip (Group B at the auxiliary intake airway side and Group C at the main intake airway side) for intensive monitoring. Based on the critical expansion deformation rate index, the pressure-relief angles were accurately determined as 61° at the open-off cut side, 58° at the final line side, 79° at the auxiliary intake airway side, and 81° at the main intake airway side, significantly improving the accuracy of boundary identification. In combination with directional long boreholes in the floor for intercepting and extracting downward pressure-relief gas, the maximum gas extraction rate reached 55.31%. The residual gas content in the protected seam was reduced to 2.29-3.90 m³/t, the permeability coefficient increased by 8-12 times, and the borehole gas flow decay coefficient decreased by approximately 40%-50%.