Located in Ela Mountain, the eastern part of East Kunlun polymetallic ore belt, the Saishitang copper deposit is one of important skarn deposits in Qinghai Province. We measured Re-Os isotopes of molybdenites which occur in skarn for the first time to understand the mineralization age, ore genesis and geodynamic environment in combination with new sulfur isotopic data of sulfides from different types of ores. Five molybdenite samples yield an isochrones age of 2245±18Ma (MSWD=015）and weighted average of 2234±15Ma (MSWD=065), indicating the deposit was formed in Late Triassic. The δ34SV-CDT values of fourteen sulfide samples range from -46‰~1‰, with an average of -173‰, suggesting the sulfur is magma-derived. The mineralization of Saishitang deposit is genetically related to the Late Triassic magmatism. Basing on the geological features of ore deposit we consider that the Saishitang copper deposit is of the skarn type. According to the geochronology data of copper polymetallic deposits in East Kunlun and the regional tectonic evolution, we conclude that the geodynamic environment of the copper polymetallic deposits in Ela Mountain are in consistent with those in the Qimantage area. The Saishitang copper deposit was formed in the post-collision environment associated with the closure of Xinghai branching ocean in Paleo-Tethyan tectonic evolution.