Abstract: The Dabaoshan Copper ore deposit is a large-sized epithermal-mesothermal hydrothermal deposit in the Xuelongshan metallogenic belt, Yunnan Province. In this study, ⁴⁰Ar/³⁹Ar dating of muscovite from ore-bearing veins containing chalcopyrite-quartz-calcite-siderite was carried out to yield a ⁴⁰Ar/³⁹Ar age of 26 ± 2.5 Ma, representing the age of the Dabaoshan Copper ore deposit. H and O isotopic analysis results show that the ore-forming fluids were dominated by meteoric water as well as minor amount of magmatic formation water. S isotopic analysis shows that the δ³⁴S values of the main metal minerals range from -5.4‰ to +1.3‰, suggesting that the ore-forming materials mainly derived from deep magma. C, H and O isotopic results also indicate that the ore-forming fluids sourced mainly from mantle magma, which was influenced by meteoric water. According to the alteration and Cu abundance of wall rocks, it can be inferred that the ore-forming material of the Dabaoshan copper ore deposit might derive from deep magma and ore-forming fluids were the mixture of magmatic water and meteoric water.