The Dongtangzi Pb-Zn deposit is one of the typical Pb-Zn deposits in the Qinling metallogenic belt. Its mineralization has been studied by many researchers, but the study has been limited by the testing methods and the level of understanding. Its material source is still a problem of much controversy. Based on the study of the geological characteristics of the Dongtangzi Pb-Zn deposit, the authors carried out S and Pb isotope analysis of related samples. The analysis included different types of lead-zinc ore. The source of ore-forming materials of the lead-zinc deposit and the relationship between magmatic rocks and Pb-Zn mineralization in the study area were discussed. The results show that the δ³⁴S value of ore sulfides varies from 1.8‰ to 12.5 ‰ with an average of 7.50 ‰, whereas the δ³⁴S_∑S value in the ore-forming fluid is 7.7 ‰, which shows the characteristics of mixed sources of sulfate in sea water (evaporation paste rock) and magmatic sulfur. The Pb isotope composition of ores is stable in this deposit, which indicates that Pb sources were mainly derived from the upper crust with rich U-Th-Pb elements and deep surroundings, which might have been related to deep magmatic activity. The results show that the metallogenic process of the Dongtangzi Pb-Zn deposit was closely related to the large-scale multi-stage tectonic-magmatic-fluid activity in the Indosinian period, and this understanding provides a new idea for prospecting in the next stage.