Abstract: In order to solve the problem of "three-underground" mining and gangue disposal in coal mine, a flexible mold slurry filling mining experimental study was carried out on the CT1305 face of Guozhuang Coal Mine. According to the surface settlement control target of filling mining, the theoretical filling rate of goaf should be not less than 80% by using the "probability integral method", and the minimum strength of flexible mode slurry filling body should be not less than 2.43 MPa by using the "strength requirement design method of cemented filling body". Multiple tests show that when the ratio of cement, fly ash, coal gangue and water is 1:3.33:9:2.35, the mass concentration of slurry is 85% and the final coagulation strength of backfill body is above 2.51 MPa, which meets the needs of pumping and filling. Moreover, multiple sets of numerical simulation results show that when the filling rate of goaf reaches 80%, the maximum surface subsidence value is 201mm, the surface horizontal deformation is 1.87 mm/m, the inclined deformation is 1.23 mm/m, and the curvature is 0.011×10⁻³ m^-1 to meet the requirements of surface settlement control. The study provides the theoretical basis and reference for the subsequent mine industrial test.