The invention discloses a nitrogen doped carbon quantum dot as well as a preparation method and an application thereof, belonging to the technical field of material science. The preparation method comprises the steps: after mixing organic acid and organic amine, directly performing a hydrothermal reaction to prepare a nitrogen doped carbon quantum dot water dispersion solution, and extracting and drying the nitrogen doped carbon quantum dot water dispersion solution to obtain a nitrogen doped carbon quantum dot solid. The size of the nitrogen doped carbon quantum dot is not more than 10 nm, the nitrogen content is not more than 50 percent, the surface of the nitrogen doped carbon quantum dot contains amino, carboxyl and hydroxyl; and the quantum efficiency is 39.8-50 percent. The preparation method is simple to operate, environment-friendly, low in equipment requirement; and the prepared nitrogen doped carbon quantum dot has excellent light emitting property, and can be widely applied to fields such as photoelectric materials, biological imaging and fluorescence probe.