In this study,several sulfur-terpyridines and ruthenium complexes designed for development of new reusable ECL sensor were characterized by electrospray multi-stage tandem mass spectrometry（ESI-MSn）with direct injection,and their cleavage fragments and fragmentation pathways under ESI conditions were analyzed.The results showed that the sulfur-terpyridine derivatives are readily protonated by positive-ion ESI-MS and the carbon-sulfur bonds of sulfur-terpyridine derivatives are easy to break during the process of positive mode of ESI-MS.Also,the cleavage ways of carbon-sulfur bonds are different.The terpyridyl ligands containing arylthio firstly decomposed from the carbon-sulfur bond attached to the aromatic carbon-sulfur bond and lost some non-sulfur fragments while the terpyridyl ligands containing benzylthio broke from the benzylic carbon-sulfur bond and lost some fragments containing sulfur.The complexes of sulfur-terpyridyl ruthenium are easy to be detected by ESI-MS in positive mode.These complexes are stable and not easy to decompose in multi-stage mass fracture.Through identification of molecular ion peaks and further comparison of isotope mass peaks with the simulation value,the structures of complexes were identified.This research not only shows that ESI-MS is simple and accurate，and is suitable to study the structures of sulfur-terpyridine ligands and corresponding ruthenium complexes,but also provides a reference for study on the structures of this kind of compounds.