The identification of dynamic parameters of bridges is essential in investigating the mechanical characteristics of bridges and in tackling problems caused by bridge vibration. In this paper, an irregular arch bridge is studied, and structural vibration responses that follow traveling vehicles are measured. The wavelet transformation (WT) technique and eigensystem realization algorithm (ERA) are adopted to identify the structure′s natural frequency, modal shape and damping ratio. The applicability of these methods in identifying the modal parameter of complicated and irregular structures is discussed. The effect of de-noising is investigated, and different responses are analyzed to study the effect of the response on the identification of the modal parameter. The results are as follows: WT and ERA give consistent results in the modal parameter, the de-noising has no effect on parameter identification when the response is obtained from the free decaying response following traveling vehicles, and identification based on different responses can improve reliability.