Abstract: In view of the application status of underground water storage space in Shendong Mining Area, in order to better understand the stability of composite dam body, samples of coal pillar + artificial composite dam body were prepared through field sampling and laboratory sample preparation, and the changes of elastic modulus, compressive strength and tensile strength of composite dam body specimens under different water content were studied. The results show that the water absorption of coal pillar + artificial composite dam body specimens increases with the increase of soaking time. The elastic modulus is mainly related to the structure of the dam body specimen, and the influence of water immersion on the compressive strength and tensile strength of the composite dam body specimen is relatively small, and the influence of water immersion on the compressive strength and tensile strength of the composite dam body specimen is lower than that of the natural curing specimen from the initial stage. With the increase of water content, the elastic modulus and compressive strength of the composite dam specimens showed a decreasing trend, while the tensile strength showed no obvious increasing trend.