Abstract: The eigensystem realization algorithm is one of the global time domain methods for modal parameter identification, and it is widely used recently for its high accuracy and fast speed. The essence of ERA is using the measured impulse response or free response to perform identification; however, the forced vibration response is more commonly desired in the real project. Based on ERA, the paper presents the extended eigensystem realization algorithm (EERA) which could be used along with the measured forced response, and improve the accuracy by the observer Markov parameter. The identification of a 3-NDOF numerical simulation via EERA demonstrates the proposed method’s validity and accuracy through the comparison among exact results, EERA results, and ERA results. Then a laboratorial shaking table test of a four-story frame structure was conducted under the excitation of El Central earthquake wave, and acceleration responses were recorded by the wireless sensing technology. The modal parameters of the four-story frame structure were identified accurately by the EERA method, showing the possibility of its application in real projects.