A method for preparation of near-infrared silver sulfide quantum dots, characterized in that the method comprises the following steps: 1) preparing hydrophobic silver sulfide quantum dots, comprising the steps of: 1-1) heating a mixed reaction system containing a silver source and a long chain thiol to 80-350 °C in a closed environment, to react sufficiently; and 1-2) naturally cooling the mixed reaction system to room temperature and then adding a polar solvent, centrifuging and washing to obtain the hydrophobic near-infrared silver sulfide quantum dots; wherein the silver source comprises one or more of silver nitrate, silver diethyldithiocarbamate, silver dihydrocarbyldithiophosphate, dioctyl silver sulfosuccinate, silver thiobenzoate, silver acetate, silver dodecanoate, silver tetradecanoate and silver octadecanoate; and the long chain thiol comprises one or more of octanethiol, undecanethiol, dodecanethiol, tridecanethiol, tetradecanethiol, pentadecanethiol, hexadecanethiol, octadecanethiol, eicosanethiol, hexanethiol, 1,6-hexanedithiol, and 1,8-octanedithiol; and 2) reacting the hydrophobic silver sulfide quantum dots in step 1) with stoichiometric or excessive amount of mercapto-containing hydrophilic reagent in polar organic solvent to allow the surface thereof to be attached with hydrophilic groups, so as to obtain the hydrophilic near-infrared silver sulfide quantum dots; the hydrophilic reagent is any one of mercaptoacetic acid, mercaptopropionic acid, cysteine, cysteamine, and ammonium mercaptoacetate or any combination thereof, wherein the near-infrared silver sulfide quantum dots have monoclinic structure and the particle size thereof is below 8 nm. 1) preparing hydrophobic silver sulfide quantum dots, comprising the steps of: 1-1) heating a mixed reaction system containing a silver source and a long chain thiol to 80-350 °C in a closed environment, to react sufficiently; and 1-2) naturally cooling the mixed reaction system to room temperature and then adding a polar solvent, centrifuging and washing to obtain the hydrophobic near-infrared silver sulfide quantum dots; wherein the silver source comprises one or more of silver nitrate, silver diethyldithiocarbamate, silver dihydrocarbyldithiophosphate, dioctyl silver sulfosuccinate, silver thiobenzoate, silver acetate, silver dodecanoate, silver tetradecanoate and silver octadecanoate; and the long chain thiol comprises one or more of octanethiol, undecanethiol, dodecanethiol, tridecanethiol, tetradecanethiol, pentadecanethiol, hexadecanethiol, octadecanethiol, eicosanethiol, hexanethiol, 1,6-hexanedithiol, and 1,8-octanedithiol; and 1-1) heating a mixed reaction system containing a silver source and a long chain thiol to 80-350 °C in a closed environment, to react sufficiently; and 1-2) naturally cooling the mixed reaction system to room temperature and then adding a polar solvent, centrifuging and washing to obtain the hydrophobic near-infrared silver sulfide quantum dots; wherein the silver source comprises one or more of silver nitrate, silver diethyldithiocarbamate, silver dihydrocarbyldithiophosphate, dioctyl silver sulfosuccinate, silver thiobenzoate, silver acetate, silver dodecanoate, silver tetradecanoate and silver octadecanoate; and the long chain thiol comprises one or more of octanethiol, undecanethiol, dodecanethiol, tridecanethiol, tetradecanethiol, pentadecanethiol, hexadecanethiol, octadecanethiol, eicosanethiol, hexanethiol, 1,6-hexanedithiol, and 1,8-octanedithiol; and 2) reacting the hydrophobic silver sulfide quantum dots in step 1) with stoichiometric or excessive amount of mercapto-containing hydrophilic reagent in polar organic solvent to allow the surface thereof to be attached with hydrophilic groups, so as to obtain the hydrophilic near-infrared silver sulfide quantum dots; the hydrophilic reagent is any one of mercaptoacetic acid, mercaptopropionic acid, cysteine, cysteamine, and ammonium mercaptoacetate or any combination thereof, wherein the near-infrared silver sulfide quantum dots have monoclinic structure and the particle size thereof is below 8 nm.