In order to study the effect of dissolution on the seepage property of broken rock, an experimental system for testing the seepage property of broken rock under the condition of mass loss was designed. The halite was added in the broken mudstone to simulate the dissolution phenomena in nature, which can accelerate the dissolution process. The evolution law of seepage property of broken mudstone under dissolution was discussed. The effects of seepage pressure, halite content, and particle size of mudstone on the permeability of broken mudstone under dissolution were analyzed. The results show that dissolution caused loss of soluble matters and fine particles in broken rock to damage the pore structure and framework structure inside that specimen easily, thereby resulting in the expansion of underground watercourse in structure and the sharp increase of permeability parameters. The permeability parameters were positively related to the seepage pressure, halite content, and particle size of mudstone. For the rock specimen with greater seepage pressure, higher halite content, and larger particle size of mudstone, the more obvious expansion of underground watercourse tended to occur due to dissolution. In addition, in the seepage process of rock specimens, the watercourse blockage caused by the particles migrations also occurred, which results in the gradual decrease of permeability parameters.