As a key factor in predicting ground-borne vibration induced by underground trains, determining the excitation forces acting on the tunnel structure is difficult by direct measurement due to their randomness, diversity, and complexity. In this paper, a novel identification method based on field measurement and an analytical track model is developed, to obtain the excitation forces acting on the tunnel structure caused by the running trains on a track. In this method, firstly, the transfer matrix between the wheel-rail contact forces and rail vibration response in the frequency domain is established through the analytical track model based on the infinitely periodic structure theory. Next, the wheel-rail forces in a reference cell are specified by the measured rail acceleration, and then the frequency-domain excitation forces acting on the tunnel structure can be calculated. Moreover, the excitation forces are obtained using a vehicle-track model for comparison to validate the proposed method. The results show that the method can effectively identify wheel-rail forces and excitation forces for the prediction of ground-borne vibration.