According to the regulation, insulating glass for construction should not have condensation or frosting problems on the inner layer during daily use. The reason for this phenomenon can be attributed to the increase in the dew point of the inner layer of the insulating glass. Therefore, dew point has become a necessary indicator to judge the quality of insulating glass. This article starts from the actual case of insulating glass condensation failure in engineering and detects the dew point of the failed product on site.