Abstract: Due to the structural sealant damage of the panel units of hidden frame glass curtain wall is located at the boundary, three new boundary-mode-based damage indexes are proposed for damage identification, including the average boundary modal assurance criterion (ABMAC), the average boundary curvature modal difference change rate (ABMCD) and, the average boundary modal strain energy change rate (ABMSE). Then, the modal test of a hidden frame panel element with a length of 2.06 m and a width of 1.46 m is carried out to study the variation of boundary modal damage index, including natural frequency and traditional modal assurance criterion with the degree of damage. The experimental results show that: when the damage degree of structural sealant is less than 5%, it is difficult to identify the local damage of structural sealant with the first six natural frequencies and the traditional modal assurance criteria; when the damage of structural sealant is 1%, the three damage indexes based on boundary modal are greater than 9%, and increased with the increase of damage, which can effectively identify the damage. Among them, the ABMCD on the damaged side is greater than that on the undamaged edge, which can be further used for the identification of damaged side.