Abstract: The artificial dam body of underground reservoir in Daliuta Coal Mine is composed of a retaining dam wall and a supporting wall perpendicular to retaining dam,and the dam structure is stable and reliable. However,the margin coefficient of the structure strength is too high,there is room for the dam structure to be optimized. The carrying capac- ity of retaining dam wall is mainly related to its skeleton structure and thickness. Since the equivalent reinforcement ra- tio of the dam skeleton structure is close to the minimum required by the specification,the structure of dam can be op- timized by changing the thickness of retaining dam wall. The ultimate carrying capacity of the retaining dam wall under the impact of water pressure and overlying vertical stress was analyzed by the orthotropic plate model. The analysis shows that with the increase of overlying vertical load,the limit head value of dam wall will decrease continuously,the stability of dam wall will be controlled by external surface strength first,then gradually by internal surface strength. The time when the variation turning point occurs is affected by the thickness of dam wall,the thinner the wall is,the earlier the turning point appears. If the water level in reservoir remains unchanged and the overlying vertical load increases continuously during the service period of the reservoir,the internal and external surfaces of the dam wall will be dam- aged successively,and the priority of damage of internal and external surface of the dam is affected by the water level in the reservoir. When the water level in reservoir is higher than the limit head corresponding to the turning point,the damage of external surface is earlier than the internal surface,and vice versa. The lower the water level in reservoir is, the longer it takes for the dam wall to break,and the better the longer-term stability of dam wall is. According to the daily water storage height of underground reservoir and the variation range of vertical load on the dam wall in Daliuta Coal Mine,it can be concluded that in the existing structure of the artificial dam,the support wall can be removed,and the thickness of the dam wall can be reduced in range from 0. 6 m to 0. 7 m,thus saving material and enhancing the economy of dam construction.