Abstract: Filling mining is a technology that can curb land subsidence, efficiently dispose of industrial solid waste, and quickly liberate the “three underground” coal resources. This article focuses on controlling mining subsidence in the 4603 (2) working face and 4604 (1) working face of Shanxi Shenzhou Coal Industry Co., Ltd. It conducts in-depth research on the determination of fly ash composition, testing of filling slurry fluidity, engineering practice of filling mining technology, and the entire process of subsidence observation. The results indicate that: ① the specialized auxiliary materials developed based on fly ash can fully stimulate the potential activity of fly ash. A flowability test mold was used to test the flowability of the filling slurry quickly, and the upper limit of the concentration of the self-flowing filling slurry was determined to be 55%. ② We have developed a bag cycle filling process with a filling step distance of 2.4 m, which includes “mining → filling → mining → filling”. We have mastered the strength evolution characteristics of filling materials at different ages and established a correlation equation between the strength of filling materials and time length. After 60 days of age, the strength of the consolidated specimens is stable at 3.0MPa, meeting the filling design requirements of 2.0 MPa for the final strength of filling materials; ③ After filling with high-concentration slurry from the terrain, the maximum subsidence of the working face is −156 mm and the maximum subsidence of the strike is −111 mm, achieving the control goal of surface subsidence less than 200 mm. This ensures the safe use of large garbage treatment stations on the ground and dense buildings and structures in surrounding coal villages. The research results can provide a reference for filling mining in similar valley mountain mining areas.