Various experimental and theoretical analyses on hydrogen evolution, absorption, and cracking behaviors were conducted to gain a fundamental understanding of the hydrogen embrittlement of high strength steel sheets with Zn-based coatings. Hydrogen evolution by H2O reduction on an exposed substrate polarized cathodically was pronounced when the galvanic couple between the coating-exposed steel substrate was formed. Hence, the hydrogen evolution and absorption behaviors are controlled by the potential differences between the coating-substrate, and the corrosion-induced damage pattern of the coating layer. These result in significant differences in hydrogen penetration and cracking behaviors between galvanized and galvannealed coated steels in a saline environment.