In this paper, the authors described the geological features of the the Dadengge gold polymetallic deposit, analyzed major elements, REE, sulfur isotope, δD_V-SMOW-δ¹⁸O_H2O, and fluid inclusions, and then summarized the geochemical features so as to find the ore-forming genesis and physicochemical conditions. Major element analyses show that the alteration zone gained SiO₂, K₂O but lost Na₂O, Al₂O₃, CaO during alteration. The sulfur isotope composition ranges between 7.0‰ and 7.1‰ δ³⁴S_CDT, suggesting that the sulfurs were of the same origin, being a unified source. The δD_V-SMOW values range from -83.68‰ to -116.95‰, and theδ¹⁸O_H2O values range from -2.57‰ to 8.35‰, suggesting that the mineralizing fluids were derived from the mixed magmatic and meteoric water. The mineralizing process took place under the condition of medium temperature (86-429℃) and low salinity (1.74%-22.38% NaCl_eq), and the mineralizing fluid might have been a CO₂-H₂O-N₂-NaCl system. The mineralizing fluids of the main mineralization stage exhibited feature of multiple sources, and the change of physicochemical conditions and fluid immiscibility were the important mechanisms for deposition and enrichment of gold and other mineralizing elements.