The long-term accumulation of coal gangue will form acidic coal gangue leachate containing heavy metals such as lead and chromium under the erosion of weathering rainwater, seriously polluting the soil and groundwater environment of the mining area. This study used bentonite, fly ash, and fly ash as raw materials, and added sodium polyacrylate to prepare bentonite fly ash fly ash sodium polyacrylate composite anti-seepage material (BFS), and investigated its anti-seepage performance.The research results found that a four factor interaction experiment was conducted by adding fly ash and sodium polyacrylate to the mixture of bentonite and fly ash. The optimal mass ratio of bentonite, fly ash, fly ash, and sodium polyacrylate obtained based on the response surface Central Composite test method was 65:35:37.5:4. At this ratio, the permeability coefficient of BFS was 1.35 × 10-8 cm/s, the cation exchange rate was 54.09 cmol+/g, and the free expansion coefficient was 8.55 mL/2g, meeting the requirements of anti-seepage performance.The development of BFS fully utilizes the advantages of fly ash and sodium polyacrylate, which has practical significance in reducing the cost of reclamation in coal mining subsidence areas, increasing the comprehensive utilization path and utilization rate of fly ash and bentonite. At the same time, it provides theoretical support for the design, application, and effectiveness evaluation of the anti-seepage layer for coal gangue landfill sites.