In view of the pitting defect on the surface of high strength galvanized sheet, the root cause of this defect from the perspective of the whole process analysis was discussed. Using the scanning electron microscope analysis, it was found that the thickness of the zinc layer on the galvanized sheet was not uniform, the surface roughness was different to a great extent and there were many surface cracks on the surface of the galvanized sheet. Tracking analysis found that the surface cracks were mainly generated in the cold rolling process. Combining with the microstructural characteristics of hot rolled plate, the mechanism of pitting defect was that the surface cracking resistance of the sheet during the rolling process was low, resulting in the formation of 10 μm depth surface cracks on the surface of cold rolled sheet. According to the simulation analysis of CCT curve, it was found that controlling the surface microstructure of the hotrolled steel sheet could significantly inhibit the occurrence of pitting defects on the surface of high strength galvanized sheet.