The metal particles and mineral phases discovered in copper slag from the Shang Dynasty Yuanqu City site give crucial information for the copper melting and casting history of early China. Optical microscope, SEM and SEM-EDS were used to analyze the major components of the slag and samples in the furnace. The distribution and forms of copper, tin, lead and arsenic were elucidated. Crystalline tin-oxide (SnO2), covelline and other copper sulfidic minerals, cuprite, malachite, small (micrometer-sized) copper or copper alloy droplets, and particles of Co or Ni oxides were found in the slag. Cu, Pb and As exist mainly in the form of small droplets in copper alloys of the slag; Sn is mainly in the form of cubic columnar or acicular tin-oxides crystal. Small amounts of Cu and Pb have been identified in the glassy phase. Analysis suggests that the slag and furnace wall are relics of copper smelting, melting and casting. Tin was intentionally added in the process of melting and casting.