The supply of metal materials for mintage is important for state governance, and the patterns of which appear to reflect the rise and decline of the central authority to some extent. Many details about this issue in the early western Han dynasty, China, still need to be verified, such as what is the pattern of metal supply for mintage and whether other sources exist in addition to the domestically exploited raw metal? In this paper, 15 early Western Han Banliang半两 coins excavated from the Guanghuacun光华村 cemetery, Chengdu city, Southwest China, were studied via scientific analyses (SEM–EDS, ICP–AES and MC-ICP-MS etc.). The results reveal three types of alloys and might constitute the first scientific identification of Cu-Sb-As alloyed ancient Chinese coins. By combining the comparisons of alloying techniques and lead isotopic ratios, with the archaeological context and historical texts, it can be inferred that many coins should be made of domestically exploited metal from the Xiaoqinling region, which was also the main provenance of the material for the Banliang coins of the Qin dynasty, while the materials of others are probably derived from the Sichuan-Yunnan-Guizhou Rhombic Block region, Southwest China, which was outside of Han’s control. This finding provides new insight into the weakness of the central government in the early stage of the Han empire and reflects the communication between the Central Plains dynasty and the culture in Southwest China in this era.