Abstract: A corrosion experiment of copper-nickel alloy immersed in 3.5 %NaCl (mass fraction)solution was conducted.The open-circuit potential and electrochemical impedance spectra and polarization curves for different periods were tested.An equivalent circuit model was established by analyzing the changes of the impedance spectrum and the polarization curve and the equivalent values of the equivalent elements were obtained by ZsimpWin fitting.The influence of Mn element on the electrochemical performance of copper-nickel alloys was studied.The results show that the open circuit potential of copper-nickel alloy samples with low Mn content (0.53 %) is more positive in the initial stage of immersion; And the open circuit potential of samples with high Mn content (1.19 %) was corrected after immersing for more than 7 days.The corrosion product film formed on the sample with low manganese content is more protective than the sample with high manganese content.The low manganese content of the alloy helps to increase the corrosion resistance of the alloy and reduce the corrosion rate of the alloy.