Objective To obtain highly corrosion-resistant coating with resistance to yellow conversion. Methods Composite passivating fluid was obtained by adding inorganic salts into the composite solution of KH560 modified by KH791 together with cationic polyurethane. Ac impedance test and salt spray test were performed with the coating after the composite passivating liquid was rolled on the galvanized sheet. The influence of the inorganic salts added on the coating corrosion resistance was studied and its reaction mechanism was inferred. Results The ac impedance spectroscopy of the cationic polyurethane composite coating displayed three time constants and in the 48 h salt spray test the corrosion area was only 1 / 8 that of the composite coating without addition of inorganic salts. Conclusion The molecular cross-linking degree was improved after KH560 was modified and the three-layer membrane structure formed by inorganic salt addition could stop the invasion of corrosive medium more effectively, so that its corrosion resistance could be obviously improved.