Abstract: To address the issues of low compressive strength, high permeability, and poor stability of conventional borehole sealing materials used in coal mine gas extraction, this study developed a novel multi-phase change gel composite material based on solid waste by utilizing a synergistic nano-chemical modification approach. The material achieves comprehensive optimization in terms of high fluidity, low permeability, and enhanced stability. The primary components of the multi-phase change gel include acrylate and sodium carboxymethyl cellulose, with auxiliary agents such as polyoxysilane crosslinkers, sodium silicate, and polyacrylamide (PAM) to facilitate the cross linking reaction. Anhydrous magnesium oxide serves as the initiator, while sodium gluconate and aluminum sulfate are used to regulate the gel setting rate. Bentonite is added as an anti-syneresis agent. In the chemical modification process, polyoxysilane condenses with the base material to form Si–O–Si bridges, enhancing thermal resistance. Sodium silicate hydrolyzes to form a dynamically cross-linked silicate tetrahedral network, improving durability under high-salt and high-humidity conditions. Polyacrylamide stabilizes water molecules through hydrogen bonding, to effectively suppress hydration shrinkage and cracking. From the perspective of physical modification, MgO particles act as physical cross linking points by electrostatic interactions, enhancing the elastic modulus. The rapid crystallization of PAM molecular chains forms a highly ordered structure, strengthening the gel network. A micro-nano dual-scale filling system is constructed using nano-SiO₂ and coal gangue powder. Through the optimization of setting time and flowability by adjusting the component ratios, the permeability, compressive strength, and microstructure of material were systematically evaluated. The results show that the material achieves a flowability of 220 mm, an initial setting time of 480 minutes, a final setting time of 580 minutes, a 28-day compressive strength of 7.5 MPa, and a permeability as low as 5.21×10⁻¹⁸ m². SEM analysis reveals that nano-SiO₂, in conjunction with C–S–H gel, effectively fills micro-cracks, resulting in a compact and pressure-resistant structure. This material combines the advantages of high performance and low cost, and is suitable for high-pressure pumping construction in drilling, effectively extending the service life of the drilling holes.