Abstract: In response to the issue of white spot defects appearing on the surface of hot-dip Al-Si IF steel strips during processing and use by customers in coastal areas, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were employed to analyze the surface and cross-sectional micromorphology and composition of the white spot defects and normal areas. The results indicated that the defective areas exhibited higher concentrations of O and C elements, along with the presence of Cl elements, which were absent in normal areas. The analysis suggests that the primary cause was excessive thickness of the passivation film on the strip coating surface, leading to the formation of cracks. In the salty and humid coastal climate, Cl^- diffused through these cracks, inducing electrochemical corrosion of the coating and resulting in white spot defects. Accordingly, corresponding improvement measures were proposed, including reducing the surface roughness of the strip, diluting the concentration of the passivation solution, and decreasing the passivation speed. These measures aimed to minimize residual passivation solution, hereby reducing the thickness of the passivation film to reduce cracks in the passivation film, and ultimately eliminate white spot defects on the coating surface.