<p>The coal mine underground reservoir is a crucial underground engineering technology, designed to store and safeguard water resources that continuously migrate underground as a result of mining activities. The artificial dam in the underground reservoir is constructed to bear the water and overlying strata pressure, whose strength is in dynamic change during frequent water storage and drainage activities. In this study, a structural concrete strength prediction function was established by conducting uniaxial compression experiments on the concrete specimens treated with wet-dry cycles. And the three-dimensional yield function of the artificial dam was constructed with the displacement variational method and Mohr-Coulomb criterion. The analyses indicated that the inner surface stability of the dam is significantly lower than the outer, while the upper corner of the inner surface is under the highest yield risk. The growth of top pressure reduces the stability of the entire dam, while the water height mainly affects the region around the inner surface. The reduction of design thickness exacerbates the stability distribution difference, contributing to the yielding expansion toward the mid-surface. As the storage and drainage cycle increases, the yield area mainly expands along the thickness direction under high top pressure and height direction under high water height or small design thickness, and the percentage of yield area reveals a rapid increase and remains stable. This research provides a quantitative reference for the safety construction, stability monitoring, and evaluation of the artificial dam in underground coal mine reservoirs.</p>