Shizishan orefield is the most representative large-size copper-gold orefield in Tongling ore district, Anhui Province. Copper mineralization and gold mineralization existed in association or fractionation either temporally or spatially. Based on systematic study of the fluid inclusion for the copper deposits and the gold deposits, the solubility of Cu, Au transportation complexes species has been calculated according to obtained thermodynamic parameters, the mechanism and the key factors to the association and fractionation between copper and gold in ore-forming fluid has been discussed. It is concluded that, in the ore-forming fluid of the Shizishan orefield, the dominant Cu complexes species were CuCl2- and CuCl0 which were affected by the concentration of Cl- anion, the dominant Au complexes species were Au(HS)¬2- and Au2S(HS)22- affected by the total sulfur concentration. The unloading and precipitation of both Cu and Au in the ore-forming fluid was controlled by temperature, pH, fO2 and fS2. The great difference of complexes species and solubility between copper and gold dissolved in the ore-forming fluid responded distinctly to physicochemical conditions, which led to their precipitation difference in time and space, and the temporal-spatial separating of copper mineralization and gold mineralization.