When hot dip galvanizing treated steel structures, a sudden temperature change is given, and unsteady thermal stress occurs in a member between a part doing a dip earlier and parts doing a dip later, and there is the case that thermal strains and crack accidents. In this paper, with introduction of three sample cases of galvanizing cracks and thermal deformation, we are illustrating our analytical studies in order to figure out thermal distribution and its incidentally arising thermal stresses near galvanizing cracks. And we add examination about mechanism and the preventive measures against hot dip galvanizing cracks and thermal deformation from a provided analysis result.