Evaluation on the buffeting performance of the long-span cable-supported bridge is the significant step for the bridge wind-resistant safety design. However， current buffeting theories are more descriptive， but not explanatory in the sense of revealing basic buffeting physical causes. In addition， the details of the fluid-structure interaction （FSI） during the buffeting are hard to be reproduced. In this work， the Sutong Bridge is selected as the research object， the buffeting responses of its numerical model are simulated in the software Fluent. And the numerical buffeting responses are compared with the theoretical ones. Results show that the forced vibration is the major component of the wind-induced vibration in the wind field with high turbulence intensity. The theoretical and numerical RMS of the buffeting responses are close when considering FSI effect. Vortex core development conducts alternatively between the upper and bottom of the deck. What’s more， signature turbulence has little effect on the buffeting responses of the model.