AbstractThe time‐domain Routh‐approximant method for model reduction of large‐scale systems is modified and enhanced in this paper. A new transformation matrix that overcomes a limitation of earlier work is proposed. This feature greatly enhances the multivariable method. Some interesting results on symmetry properties are developed in conjunction with a structure example. A sufficiency condition of stability of the reduced‐order model is identified. The response of the reduced‐order model traces the original system very well. Thus the Routh method offers promise for application in the suboptimal control of large space structures, given its inherent simplicity.