In recent years, carbon nanodot (CDs) have been widely researched due to their unique luminescent properties, good biocompatibility, low toxicity and high photostability. These characteristics invite potential applications in optoelectronic devices, visible light communication, tumor therapy, biological imaging and other fields. There are a variety of CDs according to the different starting materials and synthesis routes. In this paper, we will systematically review nitrogen-doped CDs synthesized from citric acid and urea as the main precursor materials in our group in recent years, discuss their physicochemical properties, explore the methods and principles of CDs energy band regulation, and introduce the application progress of CDs.