Abstract: Thick specification (thickness not less than 2.0 mm) hot-dip galvanized products without patterns are widely used in industries such as animal husbandry, photovoltaic brackets, corrugated pipes, and steel plate warehouses due to their high strength and good corrosion resistance. Galvanized sheet has strict surface quality requirements in the industry due to its high requirements for aesthetics and high corrosion resistance when used exposed. However, the surface of thick specification hot-based patternless galvanized sheet is prone to zinc flow lines and pitting leakage defects, which affect the aesthetic and corrosion resistance of the product. In order to improve the surface quality of thick specification hot-based patternless galvanized sheet and increase user satisfaction, an optimization plan is proposed based on the production experience of the pickling and galvanizing combined unit. Taking zinc flow pattern and pitting leakage plating as research objects, the macroscopic morphology of zinc flow pattern and leakage plating was characterized using SEM and metallographic microscope. By briefly describing the fluctuation of the shape of the raw material hot-rolled substrate, the operation status of the three rollers, the surface roughness of the hot-rolled raw material, the presence of difficult to reduce oxides or inclusions in the original plating plate after acid washing, and the factors affecting the occurrence of zinc flow pattern and pitting leakage plating defects, combined with production experience, the "double leveling" process was proposed to improve the uniformity of plate shape and surface roughness, optimize equipment stability management, zinc liquid temperature control, and effectively reducing the defect rate.