The Saidu gold deposit is located in the northwest part of Ertix tectonic zone in Xinjiang. The ore bodies occur in altered mylonite zones within the Markuli giant fault belt and are controlled by the ductile shear zone. The tectonic-metallogenic fluids of the early stage are characterized by mesothermal-hypothermal CO2-N2-rich fluids, with homogenization temperatures of fluid inclusions being 252.0~408.0℃. The tectonic-metallogenic fluids at the middle stage are characterized by CO2-H2O fluids, with homogenization temperatures being 203.0~325.8℃. The fluids at the late stage were epithermal-mesothermal low salinity aqueous solutions, with homogenization temperatures being 120.0~221.0℃. The δ34S values of pyrite in the gold deposit range from 3.53‰ to 5.88‰; the lead isotopic compositions are fairly constant, with 206Pb/204Pb ranging from 18.0997 to 18.3585, 207Pb/204Pb ranging from 15.4877 to 15.5790, and 208Pb/204Pb ranging from 38.1116 to 38.3551. Sulfur and lead isotope studies indicate that the ore-forming materials originated from the deep portion, and had close relationship with magmatic activity. The ore materials were obtained from rocks of the lower crust during the orogenic period. The main gold mineralization was related to the post-orogenic extension environment, with the evolution characteristics corresponding to the evolution of shear zones.