The modelling of swivel structures is essential when studying the fluctuations in railway environmental vibrations propagating of swivel bridge. Refined modeling of the swivel structure can effectively improve the accuracy of the results, but the modeling process is too complex to compute efficiently. To improve the calculation efficiency of swivel structures, an equivalent dynamic calculation model is proposed based on the principle of impedance equivalence in structural dynamics.Next, the equivalent calculation formula is derived, and the equivalent dynamic calculation model is established. Finally, the structural vibration response is solved by taking the measured acceleration responses as input, and its accuracy is verified by comparing the refined finite element model and the results of field vibration tests. The results demonstrate that the above equivalent dynamic calculation model can obtain relatively accurate response results, and the solution time is only 29% of the refined finite element model. Thus, the proposed equivalent dynamic calculation model has the advantages of simple modeling and fast calculation, which can provide a new modeling method for studying the wave problem of swivel bridges.