In this paper, an improved mode accuracy indicator is presented to more efficiently distinguish physically true modes from computational spurious modes generated by Eigensystem Realization Analysis (ERA) methods. Since the system order of real-life structures is a priori unknown, the number of assumed poles is usually set to be two to ten times the number of true modes in the frequency range of interests. Thus, the modal identification process could create exceedingly large number of computational modes. For the reason, it makes it difficult for analysts to distinguish the physically true modes from the spurious modes. The proposed mode accuracy indicator could better narrow down the choice of true modes than existing indicators and particularly it shows better consistency for the structure having high damping ratios. A series of numerical tests are demonstrated for verification of the proposed mode accuracy indicator. In addition, the improved mode accuracy indicator is applied to an experimental decentralized modal identification of a laboratory-size 8-panel space frame structure.