Abstract: Objective China is building large-scale salt caverns for underground storage of natural gas, compressed air and hydrogen. However, the conventional single-well construction method faces clear limitations in bedded salt. Horizontal well leaching provides a promising alternative for building large caverns in salt layers of limited thickness, yet the current understanding of the horizontal cavern expansion patterns and the influences of relevant parameters under the presence of interlayers remains insufficient. Methods We fabricated composite salt specimens consisting of pure rock salt layers and mudstone interlayers , and set up a physical simulation platform for horizontal cavern leaching. Five groups of experiments were carried out with varying interlayer configurations, water injection rates, leaching cycle periods and well spacings. Cavern morphology evolution was observed during the experiments, and final three‑dimensional cavern models were acquired by 3D scanning. The effects of interlayers and other factors on cavern expansion patterns and leaching rate were analyzed. Results Analysis of cavern morphologies during the experiments and final 3D models indicates that, interlayers inhibit upward dissolution and promote lateral expansion of the cavern, resulting in a more uniform horizontal-section cavern height below the interlayers compared with that in pure salt rock. Due to the low solubility of the interlayers, the average cavern leaching rate is reduced by 8.5% relative to that in pure salt rock. After interlayer collapse, insoluble material settled at the salt cavern floor, reducing effective gas storage space. The collapse of the lower interlayer in the sample decreased the effective volume by approximately 23% compared with pure salt rock. When the water injection rate was increased from 10 mL/min to 15 mL/min in the bedded specimens, the leaching rate improved by roughly 40% and cavern development became more symmetrical on both horizontal sides; however, the average discharge brine concentration dropped by approximately 16.5 g/L, raising freshwater consumption and energy costs. Shortening the leaching cycle period and reducing well spacing had minor effects on the leaching rate and the cavern volume, but they helped improve cavern symmetry. Conclusions The influence of interlayers on the horizontal cavern expansion process and the internal cavern space cannot be ignored. For horizontal cavern construction in bedded salt rock, parameters such as water injection flow rate and leaching cycle period must be comprehensively regulated to balance construction efficiency and the utilization of cavern space. This study serves as a supplement to existing simulation experiments that have focused primarily on pure salt rock, and can provide experimental reference for the application of horizontal cavern leaching in bedded salt formations.(Figure 14 , Table 7, Reference 24)