Developing efficient onsite damage detection and safety evaluation methods for glass curtain wall is still a challenging task. In this work, a simple approach to predict the failure and risk of falling down of curtain wall glass was developed through the relationship between the natural frequency changes and the declined reliability of the structures. Natural frequencies of the curtain wall glass under various clamping conditions were determined using dynamic tests. It was discovered that, with the decrease of the clamping force at the boundary of the glass specimen, the measured natural frequencies decreased linearly. Thus, the in-service capacity in edge clamping (e.g. boundary is loosed or failure of the supporting structure) of the curtain wall glass can be identified by its natural frequency changes. The expected lowest safety natural frequency of a curtain wall glass (given elastic parameters, shape and size) is given. The implementation of this detection method is described, and the practicability and feasibility validated.