Abstract: During coal mining in the western region of Inner Mongolia, a large amount of coal gangue solid waste is produced. The massive accumulation of coal gangue on the surface has caused serious damage to the ecological environment and poses a series of potential hazards. In this paper, coal gangue is used as aggregate, and multiple filling pastes are formulated based on the Talbol grading theory to explore which grading scheme yields filling pastes with high fluidity and strong durability, thereby providing a solution to the problems of coal gangue stockpiling and surface subsidence caused by goafs. Through fluidity and strength tests—including fluidity testing, bleeding rate testing, and compressive strength testing—the flow performance of filling pastes prepared with various particle size gradations and their compressive strength at a curing age of 28 d were examined. Through durability tests—involving the determination of density, water content, water absorption, porosity, and freeze-thaw cycle testing—the durability of filling pastes prepared with various particle size gradations was evaluated. The results show that, based on fluidity and bleeding rate tests, the larger the maximum particle size, the greater the fluidity and bleeding rate with the increase of the grading index, demonstrating stronger flow performance. Durability test analysis indicates that filling paste specimens prepared with a maximum particle size D=20 mm and a grading index n=0.45 can still maintain a relatively intact appearance after multiple freeze-thaw cycles, exhibiting good durability. In comprehensive consideration, among the filling pastes prepared with various particle size gradations, the scheme with a maximum particle size D=20 mm and a grading index n=0.45 is the optimal gradation scheme. It achieves the best compressive strength and durability while maintaining good fluidity.