Abstract: The water-leakage was common fault of quality of existing curtain wall, it made a significant impact on the normal function of the existing curtain wall. The cause of wate -leakage was complex usually, and the patching corresponding to the indoor leakage position was usually invalid, therefore the systemic appraisal to find out the machanism of the leakage was necessary.An appraisal proceed was carried out in this paper about the serious water-leakage of a typical existing curtain wall.To solve the complex and serious water-leakage, the appraisal was carried out by checking of drawing,inspecting of construction quanlity, and the testing of water-spraying.The cause of the wate-leakage was found out clearly by the thorough analysis which was made in this paper.The appraisal drew a conclusion and advisions of repairation, provided a reliable support for the follow-up repairation.The case was relevant for the design, the construction and maintaining of curtain wall by its typicality.