Infrared lead chalcogenide quantum dots (QDs) suffer fast degradation due to the easy oxidation of surface chalcogen atoms.Here,we report a trioctylphcophine-mediated surface passivation method to improve the air stability of PbS QDs.Surface mechanism study reveals an in situ surface reaction,which leads to site-selective passivation of surface S atoms with lead mono-carboxylate.The surface capping motif sufficiently protects PbS QDs from oxygen and improves their stability as well as quantum efficiency regardless of the QD size and original ligands on surface cations.The modified PbS QDs display no obvious fluorescence quenching and surface oxidization after 30 days of air exposure.The robust suriace capping also provides high compatibility of PbS QDs with polymers for optoelectronio device fabrication.The near-infrared LEDs based on the modified PbS QDs display a slight degradation of only 1.47％ from the maximum intensity after continuous operation in air for 250 hours(lifetime ＞ 10,000 h) at 0.5 W/ore2 power density,indicating the surface paseivation route is promieing strategy for promoting practical optoelectronic application of PbS QDs