Abstract: Based on the characteristics of S, Pb, O and C isotope in the Siwumuchang gold deposit in Inner Mongolia, the ore-forming material resource is analyzed. It is concluded that the S in metallic sulfides comes from the volcanic rock basin of Paleozoic marine bed. The Pb is provided by host strata and volcanic rock basin. In mineralization period, the ore-forming fluid is mainly derived from magma, with meteoric water mixed after the mineralization. The mineralization period of the Siwumuchang gold deposit ranges from Late Jurassic to Early Cretaceous.