Among the relics related to the coin casting of the Han Dynasty, the quantity of the clay-gravel molds is the largest. These consist of a clay surface layer and a clay backing layer mixed with much gravel. The surface layer was made from clay and plant ash to improve the quality of coins. The backing layer was made of clay and gravel to improve its mechanical properties and decrease the deformation of mold after firing. The production process was as follows:first, a backing layer was made of clay and gravel; second, a thin fine clay layer was made on the back as a surface layer; then the back pattern cavities of coins were made on the fine clay layer using a model. After being used for casting metal coins, the surface layer would be damaged by molten metal. A new thin layer could be made directly on the underlying surface or after the removal of the previous surface layer. The backing layer could be used many times until it broke. As a result, the production efficiency for casting bronze coins was improved.