Tinplate on silicon killed steel continuously cast and box-annealed, has a high ATC value. Furthermore, the experiment using X-ray photoelectron spectroscopy (XPS) indicates: 1) Silicon oxide layer exists on the steel surface after box annealing; 2) The silicon oxide layer is formed by deposition of silicon during the cleaning process prior to the annealing, and by selective oxidation of the silicon as a steel composition; 3) Most of the silicon oxide can not be removed during pretreatment in the electrolytic tinning process and remains between the steel surface and the alloy layer of the tinplate. The effect of the silicon oxide on the corrosion resistance of the alloy surface has been investigated. As for the flowmelting process, experimental results suggest that, in the early stage of the alloy growth, the silicon oxide prevents the nucleation and the growth of Fe-Sn alloy, but in the succeeding stage, area of the steel exposed to free tin accellates alloy growth, because Fe atoms diffuse from between alloy crystallites. Also in this stage, the alloy continuity on the steel surface is little improved because the growth is mainly vertical to the steel surface. This is the reason for the high ATC value. ATC value decreases to 1/2-1/3 by heating, but corrosion current density on the alloy surface shifts slightly. More investigation is necessary to clear up the reason for the decrease in ATC value by heating.