In order to improve the efficiency of coalbed methane extraction and reduce the risk of coal and gas outburst accidents, the modification of conventional sealing materials was carried out in this study, and the fly ash-cement-based mine sealing materials with nano-material composite were successfully developed. Focusing on the problem of leakage in coalbed methane extraction boreholes, the optimisation direction of sealing material performance is clearly proposed. The modification of cement-based sealing materials by nanomaterials was systematically studied, and the mechanism of action was revealed. The experimental data show that when the content of nano-SiO₂ and nano-metakaolin is 2% and 5%, respectively, the comprehensive properties of the materials reach the optimum, and the two nanomaterials achieve a synergistic enhancement effect through defect complementation. With the help of XRD, TG, MIP and SEM, it is clarified that nanomaterials can improve their properties by promoting hydration reactions rather than generating new products. The engineering application verification shows that the nanocomposite sealing material can significantly improve the gas extraction efficiency compared with the traditional materials.