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The invention technology is used to put zinc block into the plating aid pool regularly, so that the bivalent iron in the plating aid becomes trivalent iron, and plays an important measure to stabilize the PH value within a numerical range, and also facilitate the filter filter out the trivalent iron ions in the plating aid; Ferric ion is controlled between 0.3 and 1.0g/L; When hydrogen is not released in the plating aid, the zinc block is continued. It is an effective measure to reduce zinc slag, improve the fluidity of zinc liquid and reduce the thickness of zinc layer to play the role of plating aid filter.