The nitrogen and sulfur co-doped carbon dots (N,S-CDs) with increased luminescence were synthesized by a hydrothermal process in one green pot by using glucose,and a new sulfur-doping source of sodium sulfite was developed.The synergistic effect of the N and S groups was well discussed through the structure analysis of Fourier transform infrared spectra and x-ray photoelectron spectra.The surface states of N,S-CDs embody more complicated functional groups,and S element exists as-SSO3,-C-SO3,and SO42-groups due to the introduction of sodium sulfite.The sulfur-containing groups passivate the surface of the CDs,and the relatively high sulfur groups may reduce the non-radiation centers.The fluorescence is affected by the hydroxyl group of the solvent.The quenching of Fe3+ ion to fluorescence and the sensitivity of fluorescence to pH were also investigated.