The invention discloses application of a water-soluble fluorescent carbon dot in detection of heavy metal silver ion content. The method comprises the following steps: taking a 2mu L synthetic carbon dot stock solution, diluting to 2mL with a BR buffer solution to be taken as a fluorescent probe, exciting with 352nm wavelength light, determining fluorescence intensity of the fluorescent carbon dot probe at 441nm wavelength and recording as I0; taking an another fluorescent carbon dot probe, respectively adding different concentrations of silver ion solutions, repeating the determination step, recording as I441, and calculating linear relation between variation of the fluorescence intensity of the fluorescent carbon dot probe before and after the silver ions are added and the silver ion concentration according to the variation of the fluorescence intensity; and adding a to-be-detected sample into the fluorescent carbon dot probe, recording the variation of the fluorescence intensity at the 441nm wavelength, and calculating the mass or concentration of the added silver ions according to the linear relation. The method disclosed by the invention has an accurate heavy metal silver ion detection result, is convenient and efficient, and has good market prospects.