The work aims to obtain the best green chemical passivation process of cadmium plating layers by studying the electrochemical properties of green chemical conversion films of cadmium plating layers. The cadmium coatings were electroplated on the surface of 30CrMnSiA steel through the cyanide-free cadmium plating process, and the green passivation treatment was performed on the cadmium coating on the surface of 30CrMnSiA steel in the solution containing phytic acid and sodium molybdate, then a composite chemical conversion film was constructed on the surface of the cadmium layer. After the effects of sodium molybdate concentration, phytic acid concentration and treatment time on the electrochemical properties of the green passivation cadmium plating layer were studied in 3.5wt.% NaCl solution, the green chemical passivation process of cadmium plating layer was obtained. When the treatment time was 10 min and the concentration of phytic acid was 1.0wt.%, with an increase of 3% in the concentration of sodium molybdate, the open circuit voltage value of the sample first increased from ?0.741 9 V to ?0.739 7 V, and then decreased to ?0.761 1 V. And the charge transfer resistance Rct value and corrosion inhibition rate also increased from 2.34 kΩ.cm2 to 8.79 kΩ.cm2 and 72.9% to 92.8%, respectively, while its self-corrosion current density Jcorr first decreased from 81.47 μA/cm2 to 6.887 μA/cm2. If the concentrations of sodium molybdate and phytic acid were 2.0wt.% and 1.0wt.%, respectively, with the increase of treatment time, the open circuit voltage value of the sample increased from ?0.755 9 V to ?0.729 5 V. Its Rct value first increased to 6.68 kΩ.cm2, and then decreased to 5.28 kΩ.cm2, while its self-corrosion current density decreased from 16.26 μA/cm2 to 4.527 μA/cm2. When the concentration of sodium molybdate was 2.0wt.% and the treatment time was 10 min, with the increase of phytic acid concentration, the open circuit voltage value of the sample decreased from ?0.739 3 V to ?0.756 1 V. And its Rct value first increased to 6.68 kΩ.cm2, and then decreased, while the self-corrosion current density Jcorr value first decreased to the minimum value and then increased. Compared with the cadmium coating, the samples treated with the chemical conversion coating have higher open circuit voltage, larger charge transfer resistance and lower self-corrosion current. The green passivation process for the surface of cadmium coating has good corrosion resistance and low cost concentration. The sodium molybdate and phytic acid are 2.0wt.% and 1.0wt.%, respectively, and the treatment time is 10 min.