Abstract: Upstream wet tailings dams exhibit a continuous increase in accumulation height during its construction and closure, elevating the risk of dam failure. To analyze the short-term stability of heightening in a large tailings dam in Northeast China, core samples are obtained from critical dam profiles, and combined with geotechnical tests to analyze tailings deposition patterns within the dam. Further, hypotheses regarding tailings particle distribution are proposed, and a generalized model for dam crest elevations ranging from 485 to 521 meters is derived, considering the most unfavorable seepage water levels. ABAQUS is employed to conduct numerical simulations analyzing the slope stability of the tailings dam under varying dam crest elevations. Research findings indicate a sedimentation pattern characterized by coarser particles settling first, followed by finer particles. Tailings near the dam front primarily consist of tailings silt, while those deeper within the dam predominantly comprise tailings powder soil/clay. Spatially, consolidation of tailings increases gradually from far to near and from top to bottom within the dam, while temporally, the compactness of tailings increases with deposition time. During the process of raising the dam crest elevation from 497 to 521 meters, the maximum vertical displacement of the dam crest under normal and flood water levels increases by 28% and 38%, respectively, resulting in a decrease in the dam body’s safety factor by 1.6% and 2.1%, respectively. The rise in water level contributes to a decrease in the safety factor, while dam deposition exacerbates this effect. Consequently, it is recommended to strengthen monitoring of dam displacement and infiltration lines during the heightening process, implement additional drainage measures to lower water levels within the dam, and mitigate the influence of seepage on the stability of the tailings dam. The research outcomes serve as a foundation for developing preventive measures against deposition risks in tailings dams.