The work aims to investigate the corrosion inhibition performance of carbon dots (CDs) for different metals under different conditions and then analyze the action mode of CDs in solution, put forward the inhibition mechanism model and explain the differences between CDs and traditional corrosion inhibitors in action mechanism. CDs were synthesized by hydrothermal method, and weight loss tests, electrochemical measurements and surface analysis were adopted to study the inhibition performance of CDs on carbon steel and aluminum alloy in CO2-saturated 3.5% NaCl solution and 0.1 M hydrochloric acid solution, respectively. CDs could inhibit the corrosion of carbon steel and aluminum alloy effectively. From the weight loss tests, the inhibition efficiency received 93% and 86%, respectively when the adding concentration was 50 mg/Land 5 mg/L. In addition, the desorption potentials occurred obviously in anodic polarization curves, confirming the adsorption of CDs on metal surface. The morphology characterization revealed that CDs had a nano-structure protection film with thickness more than 100 nm at metal interface, thus improving the surface hydrophobicity. From the results of EIS and fluorescence microscopic observation for different immersion time, the time required to stabilize corrosion inhibition in solution was obviously longer than that of traditional corrosion inhibitors, about 3 h. CDs is an effective nanomaterial corrosion inhibitor, and the unique structure enables nanoparticles to adsorb or chelate on metal surface, and the special fluorescence properties provide a new idea for in-situ characterization of adsorption processes.