Abstract: Horizontal-well leaching is an inevitable development trend of salt-cavern gas storages in China, and the bottleneck restricting its development is that the morphological development law of salt cavern has not been clarified. In this paper, a simulation experimental instrument for horizontal-well leaching was developed to carry out tests. In the process of tests, the morphological propagation process of salt cavern was observed in real time. A set of synchronous sampling device for brine mass fraction was developed, which can realize brine sampling at different parts of the salt cavern at the same time. The relationship between the distribution law of brine mass fraction inside the salt cavern and the water injection rate was studied. Moreover, the morphological propagation law of salt cavern and its causes were analyzed. The research results provide technical support and reference for the large-scale application of horizontal-well leaching technology.