This paper studied the dynamic response of a tunnel structure under short-time impulse force excitation and identified the modal parameters. First, the precision and frequency domain feature of the short-time impulse force excitation under the actions of different hammering were analyzed. Second, the short-time impulse force excitation was applied in an in-site vibration test in a shield tunnel of Shanghai metro line 12. Finally, the frequency response functions between the impulse force excitation and the vibration response at measured points of the tunnel were carried out and combined with random decrement, orthogonal polynomial, and ARMA methods, in order to effectively identify the modal parameters of the tunnel structure. The results showed that the low and medium frequency transmission of the vibration signal was quite good, and the transmission distance was long. The modal frequency of the tunnel structure was obviously presents low frequency characteristics, and the first ten model frequencies were under 100 Hz. As a result, the short-time impulse force excitation can be applied to a tunnel vibration test and the identification of its modal parameters. It can provide effective support and a reference base for tunnel structure identification and structural health monitoring based on the modal characteristics.