Abstract：Dissolved organic sulfur （DOS） is an important component of dissolved organic matter in municipal wastewater. DOS of effluent from wastewater treatment plant has an important impact on the migration and bioavailability of heavy metals in receiving water， as well as the reuse and advanced treatment of wastewater. However， little is known about the concentration and transformation characteristics of DOS in wastewater treatment processes. In this study， high-resolution plasma mass spectrometry （HR-ICP-MS） and Fourier transform ion cyclotron resonance mass spectrometry （FT-ICR-MS） were used to investigate the concentration and molecular transformation characteristics of DOS in a typical wastewater treatment plant （anaerobic/anoxic/aerobic + coagulation sedimentation + denitrification filter + sodium hypochlorite disinfection）. The results showed that the average DOS concentration of wastewater treatment process was 42.2~167.9 μg·L-1， which was an important source of DOS in receiving water. The coagulation sedimentation tank had the highest average contribution rate to DOS removal （101.4%）， followed by the anaerobic tank （65.0%）. The average contribution rate of the aerobic tank and denitrification filter to DOS removal was -53.1% and -56.7%， respectively. The anaerobic tank mainly removed CHOS compound， converting unsaturated fatty CHOS molecules into highly unsaturated ones， and generating macromolecular CHONS（P） compounds at the same time. The peptide-like CHONS（P） compounds had the highest relative abundance in the effluent of aerobic tank. The coagulation sedimentation tank could reduce the peptide-like CHONS（P） compounds produced by the biological treatment unit， however， the denitrification filter would release the peptide-like CHONS（P） compounds due to the existence of microbes. The biological treatment section （anaerobic/anoxic/aerobic） converted the anionic surfactants with O3S1 structure into degradation products with O5S1 structure. The aerobic tank and denitrification filter mainly produced peptide-like compounds with O6-12S2N4 structure. This study can provide molecular-level information for understanding the transformation mechanism of DOS in actual wastewater treatment process， and provide theoretical guidance for the control of effluent DOS in wastewater treatment plants.