In response to the problem that the cadmium plated steel parts such as aircraft supports and bolts are prone to black spots on the surface during turnover/assembly in rainy summer, the work aims to identify the cause of black spots and formulate improvement measures by analyzing the surface composition of the cadmium-plated layer. The macroscopic morphology of the black spots and normal areas on the cadmium-plated layer was observed and the surface composition was analyzed by the scanning electron microscopy and the energy spectrum. The effectiveness of the improvement measures was verified through comparative tests on resistance to wet and heat corrosion, including pre-treatment of cadmium electroplating, chromate passivation, and temporary protection. Through surface energy spectrum composition analysis, the absence of Cr in the black spot area confirmed the discontinuity of the cadmium-plated chromate passivation film, and the abnormal content of Al element confirmed that the residual sand blowing medium in the pre-treatment caused the discontinuity of the cadmium layer. Through the verification of wet and hot corrosion resistance in both cadmium plating and non-passivated states, as well as the application of F-35 anti-rust oil test, it was determined that improvement measures such as thorough cleaning of pre-treatment sand blowing medium residues and aging of cadmium-plated chromate passivation film could ensure the integrity of the cadmium-plated layer and passivation film. Temporary protection with F-35 anti-rust oil could effectively improve the corrosion resistance of the cadmium-plated layer. The process control on pre-treatment before plating, cadmium plating, and post-treatment plays a decisive role in the quality of cadmium-plated layer, effectively protecting the parts during manufacturing and turnover and is crucial to maintain the integrity of the coating continuously. The temporary protection such as anti-rust oil can effectively improve the protective performance of the layer.