Abstract: Carbon dots (CDs) can be used as corrosion inhibitors due to their fascinating properties. In this study, nitrogen-doped carbon dots (N-CDs) with different morphologies and structures are synthesized using ammonium citrate as the raw material, and the N-CDs are prepared by pyrolysis method at 180℃ for different time (1 h, 1.5 h and 2 h). N-CDs with different morphologies are synthesized and the effect of the preparation conditions on their performances as corrosion inhibitors for Q235 carbon steel is analyzed. The corrosion inhibition mechanism of N-CDs is studied by using polarization curves, electrochemical impedance spectroscopy and surface analysis techniques. When the pyrolysis time is 1.5 h, the inhibition efficiency (IE) of N-CDs reaches the highest, and the IE of 200 mg/L N-CDs1.5 in 1 M HCl solution reaches 91.6%. As a mixed-type corrosion inhibitor, N-CDs could effectively inhibit the anode and cathode corrosion reactions of carbon steel, forming a protective film via physical and chemical adsorption, and also improve the hydrophobicity of the metal surface. In this way, the corrosion initiation and development are effectively inhibited. This study provides new ideas for the development of efficient and green corrosion inhibitors.