The safety and stability of tailings ponds are crucial for ensuring the underground collaborative mining. To investigate the impact of tailings ponds on mine engineering, this study takes a certain lithium-containing kaolin mine as the research object, and uses the GTS/NX and FLAC3D coupling modeling method to establish a three-dimensional geological-structural model. It conducts optimization of the sealing length of the +225m horizontal shaft within the inundation line of the tailings pond and analyzes the influence of the tailings pond on the stability of the ore body mining. The results show that under different sealing lengths, the stress, displacement and plastic zone of the surrounding rock of the horizontal shaft change significantly. The optimal sealing length is 105 m, at which the tensile stress at the shaft opening drops to 0.20 MPa, the displacement deformation is 8 mm, and no plastic zone is generated in the sealing area, which can effectively control the water pressure of the tailings pond and ensure the stability of the horizontal shaft. By comparing the mechanical responses of ore body mining under the conditions with and without the tailings pond, it is found that the tensile stress of the roof of the mined-out area decreases from 0.87 MPa to 0.84 MPa, the displacement decreases from 15 mm to 14 mm, and the plastic zone of the mined-out area does not connect with the surface and the plastic zone of the tailings pond. Therefore, under the current engineering and geological conditions, the tailings pond is not the dominant factor for the stability of ore body mining. The research results can provide method references and data support for the collaborative safety design and assessment of tailings ponds and underground mining in similar mines.