There are great disputes about the metallogenic age, source of ore-forming material and genesis of the Tongchang copper-iron deposit, which limits the establishment of its metallogenic model and further prospecting practice. Re-Os isotope of chalcopyrite is used to date the ore-forming age, and the S isotope compositions of chalcopyrite, pyrite and pyrrhotite are systematically studied by LA-MC-ICP-MS. The Re-Os isotopic isochron age of the five chalcopyrite samples is 484±34 Ma (MSWD=8.7), indicating that the Tongchang copper-iron deposit was formed in the Early Paleozoic Caledonian period. The δ34S values of chalcopyrite (+9.75‰-+13.1‰) and pyrite (+9.22‰-+13.9‰) in the upper part of Tongchang copper-iron deposit are slightly higher than those of chalcopyrite (+8.66‰-+10.9‰), pyrite (+8.85‰-+11.0‰) and pyrrhotite (+7.93‰-+9.28‰) in the lower part. The δ34S∑S value in the early ore-forming hydrothermal solution is about +10.6‰, and that in the late ore-forming hydrothermal solution is about +12.3‰, showing that the sulfur source of the deposit is from mixture of mantle sulfur and seawater sulfur. Thermochemical sulfate reduction (TSR) plays an important role in the process of seawater sulfate reduction. The formation of the Tongchang copper-iron deposit can be divided into two stages. In Neoproterozoic Jinning period, Rodinia supercontinent breakup event leads to submarine volcanic eruption and the formation of initial source bed which was enriched in Fe and Cu. During the Caledonian period of Early Paleozoic, the continuous cracking and rifting of the continental margin formed the Mian-Lue trough and led to intense magmatic activity. The magmatic hydrothermal solution enriched in volatile and sulfur, mixed with seawater sulfur, and extracted Fe, Cu and partial sulfur source from the spilite of the Guojiagou Formation. The early ore-forming hydrothermal solution formed the iron ore body in the deep part of the Tongchang area. With the precipitation of magnetite and sulfide, the ore-forming hydrothermal solution evolved to the late stage and migrated upward along the fault to form the copper deposit in the upper part of the Tongchang area.