Order estimation and spurious mode elimination concerning the subspace identification technique are discussed in this paper. To avoid underestimating the state space model order, order estimate is given in terms of component energy index rather than matrix singular values. Component energy index is introduced to measure the energy contribution of signal components. Based on order estimation, spurious modes resulting from noise and model redundancy are indicated by an alternative stabilization diagram which reflects the variation of parameter estimates with row increments of the Hankel matrix. Two numerical examples and one experimental example on the parameter estimation of a cable-stayed bridge model are presented to demonstrate the efficacy of component energy index and the alternative stabilization diagram.