Abstract: An online method of identification of dynamic characteristics only using measured ambient response of structural dynamic system is widely focused on.The Ibrahim and ARMA(AutoRegressive Moving Average)methods are basic identification methods.A model on dynamic system suffered by random ambient excitation was researched into, and a subspace decomposition method being different from traditional harmonic retrieval method was introduced.Robustness and effectiveness of this approach on identification of vibration characteristics are demonstrated on numerical experiment.

Key words: modal identification, system identification, structure dynamic system