The dynamic behaviors of shield tunnel are influenced by the coupling interaction between the tunnel lining structure and soil behind lining wall. In order to analyze the tunnel-soil contact coupling mechanism, a shield tunnel in Shanghai metro is selected as study case; the Bucket method is used to analyze the modal characteristics of the tunnel structure under the two different types of contact couplings including node contact coupling and foundation contact coupling. The analysis results are compared to the tunnel modal characteristics extracting from the in-site vibration test data. The results show that constrained by soil coupling, the tunnel structure presents a low frequency characteristic, the first tenth order modal frequencies range are between 0 and 100 Hz, and the modal shape amplitudes are on the order of 10?4 m. And the most important is that there is a small error between the elastic foundation contact and the measured modal characteristics, which can be applied to simplifying the model of dynamic analysis of tunnel structure, and also provide a basis for tunnel structure damage identification based on the modal characteristics.