Abstract: The fragile ecological environment and the extremely scarce water resources in the western mining area of China have become the key factors limiting the scientific development of China's coal industry. The coal mine underground reservoir represents a significant technical instrument for the protection and utilization of coal mining water resources in the western mining area. The safe operation of this reservoir is of paramount importance for the protection and utilization of mine water resources in the mining area. The stability of the coal pillar dam body is the fundamental guarantee for the safe operation of the coal mine underground reservoir. Accordingly, this study concentrates on the Shigetai Coal Mine underground reservoir in the Shendong mining region. This paper proposes a method for evaluating the stability of coal pillar dams based on theoretical research, and constructs a model for assessing the stability of underground reservoirs in coal mines. The model is subsequently employed for the evaluation and assessment of the stability of coal pillar dams, with a particular focus on those within Shigetai’s underground reservoir. The findings indicate that a comprehensive evaluation method of coal pillar dam stability in underground water reservoirs in coal mines, based on a hierarchical analysis method and fuzzy theory, was proposed. A system of evaluation indices for the stability of coal pillar dams in underground water reservoirs in coal mines was established, comprising 4 criterion layers and 14 indicator layers. The 4 criterion layer evaluation indexes were dam parameters, water flooding, coal seam endowment conditions, and mining impacts. The 14 indicator layer evaluation indexes were dam width, dam height, water blocking capacity, dam strength, water quality conditions, head height, seepage, water storage time, and coal seam inclination angle, depth of coal seam, nature of coal rock, production disturbance, mining distance of lower coal seam, and structure shape of air-mining zone. The evaluation standard of each evaluation index was provided, the membership function of trapezoidal distribution was established, and the membership degree of each evaluation index was determined. The evaluation index evaluation matrix was constructed based on the experts' evaluation, and the weights of each evaluation index were derived. Thus, the stability of the coal pillar dam body of the underground water reservoir of Shigetai Coal Mine was evaluated. The result was that the stability of the underground water reservoir dam was stable. The identified deficiencies have prompted the implementation of targeted preventive and control measures. It is recommended that grouting anti-seepage reinforcement of the seepage point be carried out in the near future, that the monitoring of the coal pillar dam body be strengthened in the medium and long term, and that the width of the coal pillar dam body be increased in the future planning of the coal mine underground water reservoir.