Abstract: The technology of underground reservoirs in coal mines has transformed water hazards into water resources, providing an effective approach for water resource protection, utilization and ecological restoration in coal mining areas with fragile ecosystems in Western China. Meanwhile, the stability of artificial dams is a necessary condition to ensure the safe operation of underground reservoirs. Therefore, in view of the reinforcement effect of bolts on the artificial dams of underground reservoirs in coal mines, based on the FLAC^3D numerical simulation method and the Pile structural element improved by the trilinear model, a numerical model of the water-retaining dam body of the underground reservoir in coal mine under the anchoring effect is established, and the influence law of bolt reinforcement on the deformation characteristics of the artificial dam body is analyzed. The research results indicate that the modified and improved model divides the bond-slip curve into the linearly elastic ascending stage, the linearly elastic descending stage and the horizontally straightened stage, which is more in line with the actual engineering situation. Meanwhile, the bolts are subjected to axial forces and shear forces, with the maximum shear force reaching 2.88 kN and the maximum bending moment reaching 273.8 N·m. Under the action of the bending moment, the bolts undergo a certain degree of bending deformation along the water immersion direction. Under the condition of bolt support, the maximum deformation of the artificial dam body is 149 mm, while under the condition without support, the maximum deformation of the artificial dam body is 160 mm, which is relatively reduced about 7%, indicating the anchoring effect of bolt support on the artificial dam body. The research results lay a solid foundation for the construction and safe operation of the dam body of the underground reservoir in coal mine.