A carbon dots with blue light was synthesized by the N and S co-doped hydrothermal method. After a series of optical and micro-structural characterizations, N and S elements could be sufficiently doped by means of the heteroatom and functional groups on the surface of the carbon dots, which decided as-prepared carbon dots to emit blue color fluorescence with the highest quantum yield of 54.27%. Owing to the strong fluorescence, the as-prepared carbon dots can be used as a sensing probe for the detection of Ag⁺ and Fe³⁺ with high sensitivity and selectivity. Both ions possessed different quenching mechanism and limit of detection with the variation of the ionic concentration through the fitting by Stern-Volmer equation, providing a new approach for efficient detection of Ag⁺ and Fe³⁺ for the application.