To separate spurious and physical modes, the classical stochastic subspace identification method had been alternated. The traditional Hankel matrix was replaced by a reformed one. Accordingly, the alternative stabilization diagram shows the variation or stabilization of the modal parameters with the row increments of the reformed Hankel matrix. The so-called component energy index (CEI), which indicates the vibration intensity of signal components, had been used as a pole stability criterion. In the stabilization diagram, spurious modes are of low CEI and unstable, while the physical ones show opposite performance. More spurious modes could be removed and the diagram illustrates the stable poles more clearly. It helps to attain more accurate estimates. The proposed stabilization diagram is performed to a simulated 4-DOF system with two close modes and small signal to noise ratio (SNR). The estimated results demonstrate that the alternative one has helped to provide an effectual and practical tool for output only modal parameters identification.