Abstract: To address the sealing failure of large-diameter gas extraction boreholes caused by surrounding rock stress deformation, a solid-liquid two-phase sealing technology is proposed. This technology aims to enhance the fracture radius of boreholes, improve gas permeability in coal seams, and simultaneously increase long-term sealing integrity and gas extraction efficiency in soft coal seams. The characteristics of non-solidified paste grouting materials are analyzed, and a multi-level composite sealing structure is constructed using expansive cement and non-solidified paste to establish a “three-segment, two-injection” sealing model. The fracture zone radius of boreholes is determined through theoretical analysis. The coupling relationship between paste viscosity（0.001-0.150 Pa·s） and grouting pressure（0.8-1.5 MPa） is simulated using Comsol Multiphysics software. A bag-type grouting device is designed to achieve timed, segmented, and multiple injections. Ultimately, a complete set of sealing equipment for large-diameter gas extraction boreholes is developed, realizing a “solid-seals-liquid, liquid-seals-gas” sealing mode, with field comparative validation tests conducted. Numerical simulations indicates optimal grouting parameters of 1.2 MPa pressure and 0.010-0.030 Pa·s viscosity, achieving a grout penetration radius of 0.91-2.22 m （covering the theoretical fracture zone of 0.88 m）. Field tests demonstrates that boreholes using this technology exhibited significantly reduced gas volume fraction decay rates, maintaining levels above 55% for 60 days—a 25% improvement over traditional cement/polyurethane sealing methods—with supplementary grouting increasing gas volume fraction by 10%. Practice proves that the solid-liquid two-phase sealing technology effectively resolves sealing challenges in large-diameter boreholes by dynamically compensating for stress-induced deformation cracks. The optimized parameter combination and segmented grouting process significantly prolong gas extraction cycles, enhance gas extraction volume fraction, and reduce decay rates, providing a reliable technical solution for high-gas mines.