Abstract: Stripe defects appeared on the surface of alloyed hot-dip galvanized gapless atomic steel. The cause of stripe defects was analyzed by macroscopic observation, chemical composition analysis, scanning electron microscopy analysis, metallographic examination, on-site investigation. The results show that there were residual degreasing agents on the surface of the steel plate during the production process of the cleaning section, which led to the formation of unrecrystallized structure on the surface of the steel plate, accelerated the diffusion rate and average growth rate of zinc and iron elements in the grains, resulting in fewer “volcanic crater” morphologies and smoother coating in the local zinc iron alloy coating. The differences in coating surface morphology caused macroscopic light reflection differences, ultimately led to stripe defects.