The vegetable tanning agent extracted from Coriaria nepalensis bark was used as raw material, and the combined tanning of pickled sheep skin was carried out with aluminum salt. The tanning process was optimized to establish a combined tanning method of Coriaria nepalensis bark tanning agent, and the leather performance and tanning mechanism were studied. The results of the experiment show that when the amount of vegetable tanning agent is 15%, the amount of Al3(SO4)2•18H2O is 20%, the penetration pH is 4.0, and the combined pH is 4.5, the shrinkage temperature of the tanned leather can reach 110.5 ℃. The tanned leather has good appearance properties, and thickness increase rate is 82.2%, tensile strength is 10.0 MPa, tear strength is 52.5 N/mm, elongation at break is 76.8%, which is better than the leather tanned by the combination of a commercially available valonia vegetable tanning agent. After tanning, the collagen fibers of the leather become thicker and form a tight network structure. The Coriaria nepalensis bark vegetable tanning agent and aluminum salt can fully penetrate into the collagen fibers of the leather and produce hydrogen bond cross-linking with them. During the combined tanning process, the aluminum salt is complexed with the tannins combined in the leather collagen fibers, which enhances the cross-linking effect, thereby significantly improving the thermal stability and mechanical properties of the tanned leather.