Curtain-wall systems in office buildings have repeated joints between units, which cause unintentional infiltration. It means that air-tightness of curtain-wall systems is directly related to building energy performance. Many countries have already enhanced air-tightness performance demands through Energy Code. In this study, a variety of air-tightness performance criteria and mock-up lab test results of curtain wall systems were analyzed. As results, air-tightness performance criteria for curtain-wall systems are suggested as follows. DIN EN 12153 and DIN EN 12207 are used as a comparison tool to analyze present states of fixed lights and opening lights in domestic buildings with curtain wall systems. According to the analyst, we suggested that Class A4 is suitable for fixed lights and Class 4 is suitable for opening lights of curtain wall system.