Abstract: To investigate the influence of mudstone content and curing age on the mechanical properties and permeability characteristics of mudstone-slag-based water barrier materials, using waste sandstone from open pit coal mine stripping was used as aggregate and mudstone and slag were used as cementing materials to make mudstone-slag-based water barrier materials. Uniaxial compression tests, gas permeability tests, and scanning electron microscopy tests were conducted on mudstone-slag-based water barrier materials, water barrier materials with mudstone mass fraction of 20%, 40%, 60%, and 80%, respectively. Based on the uniaxial compressive strength and permeability obtained from the test, we investigated the influence mechanism of mudstone content on the mechanical properties and permeability characteristics of mudstone-slag-based water barrier materials, analyzed the evolution law of the mechanical properties and permeability characteristics of mudstone-slag-based water barrier materials under different curing age conditions, and supplemented with scanning electron microscope tests, studied the characteristics and morphological features of different cementation products in mudstone-slag-based water barrier materials, and studied the influence of mudstone proportion on the macroscopic damage forms of mudstone-slag-based water barrier materials. The influence of the content of mudstone on the macroscopic damage form of mudstone-slag-based water barrier material was investigated. The results show that the uniaxial compressive strength and permeability of mudstone-slag-based water barrier materials decrease linearly with the increase of mudstone content. With the increase of curing age, the uniaxial compressive strength of the mudstone-slag-based water barrier material increases exponentially, while the permeability decreases exponentially. With the increase of the mudstone content, the gel in mudstone-slag-based water barrier material is gradually transformed from the slag gel with high strength, strong brittleness and many pores to the dense mudstone gel without microcracks. As the content of mudstone increases, the overall damage of mudstone-slag-based water barrier materials decreases and the integrity of the specimens increases; as the curing age increases, the damage of mudstone-slag-based water barrier materials increases and the integrity of the specimens decreases.