Abstract: The Xiaodongdagou gold deposit is located in the Wangjiadian-Tianhexing polymetallic metallogenic belt in the eastern section of northern margin of the North China plate, with orebodies controlled by fault structures. The mineralization is closely related to the dikes of granite porphyry and diorite. Study on fluid inclusion indicates that the ore-forming fluid in the main metallogenic stage is characterized by medium-low temperature (180-240℃), low salinity (8%-11%) and low density (0.92-0.98 g/cm³). The analysis result of hydrogen and oxygen isotopes shows that the ore-forming fluid is mainly from juvenile water in mantle mixed with later atmospheric precipitation. The sulfur is originated from magma based on sulfur isotope analysis. Considering the regional geological background and analysis results, it is believed that the Xiaodongdagou gold deposit of medium-low temperature hydrothermal vein type is the product of continental marginal magmatic arc activity formed by the subduction of the marginal Pacific Plate to Eurasia continent.