Objective To develop corrosion electrochemistry method with spatial resolution. Methods Pure Ni and Ni-P alloy coatings on copper substrates were fabricated by electrodeposition. Scanning Electron Microscopy (SEM) and XRD were applied to check surface morphology and crystal structure of the alloy coatings. Scanning Electrochemical Microscopy (SECM) research was applied to monitor the failure behavior of typical Ni and Ni-P coating in different concentration of NaCl solution. Combined with COMSOL Multiphysics simulation, 2D and 3D models were built to quantify activity point size and feedback mechanism. Results The low concentration of chloride ion had the activation effect for pure Ni coating, while higher chloride ion concentration promoted corrosion occurrence. Ni-P alloy coating maintained good stability in a short immersion time in low concentration of chloride in the solution. After 6 hours soaking, there were typical active points and corrosion products for low P alloy coating, while after 24 hours soaking for high P alloy coating. The corrosion type for low P alloy coating in 0.1 mol/L NaCl solution was localized corrosion and uniform corrosion in 0.3 mol/L NaCl solution. The simulation results of approaching curve showed that the electrochemical process of corrosion products for FcMeOH was completely inert and fresh Cu surface was electrochemical activity. 3D simulation results showed that active points of Ni-P coating failure process were close to 10 micron. Conclusion The failure process including the formation of active points, the generation and accumulation of corrosion production of Ni and Ni-P coating in NaCl solution is dependent on the positive and/or negative feedback effect of SECM mapping. Chloride ion promotes occurrence of corrosion process, and its concentration has a strong effect on the corrosion type for Ni-P coating. COMSOL multiphysics simulation results indicate that the feedback effect is strongly dependent on the distance between the tip and the substrate, and the size of active point for Ni-P coating is micron level.