Abstract: To address the rapid sealing requirements of goaf areas in coal mine double-entry roadheader operations, this study proposes a paste material composed primarily of industrial solid waste furnace slag as the main aggregate, supplemented with powdered materials such as fly ash and cement, and mixed with J85 accelerator in appropriate proportions, as an alternative to conventional sealing wall construction methods. By testing the strength properties of furnace slag-based paste materials incorporating J85 accelerator, this study reveals the effects of different filling ratios on the mechanical properties of the J85 accelerator-containing furnace slag-based paste. The results indicate that the maximum compressive strength of the furnace slag-based filling body is achieved at a ratio of 1∶2∶2 and a mass concentration of 70%, with uniaxial compressive strengths of 4.13, 6.53 and 9.75 MPa at 3, 7 and 28 days, respectively, and a tensile strength of 1.174 MPa at 28 days. As the proportion of furnace slag increases, the maximum mass concentration of the paste required for transportation decreases, and the uniaxial compressive and tensile strengths of the furnace slag-based filling body also decrease. There is a significant difference between the tensile and compressive properties of the furnace slag-based filling material, with the indirect tensile strength being only one-quarter to one-tenth of the uniaxial compressive strength. This strength disparity is primarily attributed to the inherent brittle nature of the material, which exhibits a typical mechanical characteristic of low tensile capacity compared to compressive load-bearing capacity. This is due to the porous structure, low density, and hygroscopic nature of furnace slag, which lead to inferior mechanical properties in the furnace slag-based paste filling body. The findings of this study provide a reference for constructing sealing walls using furnace slag-based paste filling materials.