To study the wind characteristics at a bridge site in the complex mountainous terrain and their effect on the buffeting response of a long-span bridge， a cable-stayed bridge in a mountainous area was considered as the engineering background. Firstly， the fluctuating wind field characteristics at the bridge site with enough monitoring points were obtained by the large eddy simulation method. Then， the buffeting forces of the bridge were calculated by the fluctuating wind field via the traditional harmonic synthesis method， the type C suggested in the specification， and the large eddy simulation method， and their buffeting responses were compared and analyzed. Furthermore， the effects of non-uniform wind field characteristics at the bridge site on the buffeting response of the bridge were investigated. The results show that the mean wind speeds， wind attack angles， turbulence intensities， etc.， of the long-span bridge in the mountainous terrain， show obvious non-uniformity along the bridge span， and the turbulence intensity ratio， fluctuating wind speed spectra， and coherence function are different from the recommended values in the specification， reflecting the limited applicability of the recommended values in the specification in complex mountainous wind fields. The buffeting response obtained by the fluctuating wind field simulated with the harmonic synthesis method is less safe than that obtained by the fluctuating wind field synchronously monitored by the large eddy simulation method. The buffeting response obtained by the fluctuating wind field simulated by the spectrum suggested in the specification is unsafe in the vertical displacement but conservative in the lateral displacement and torsional displacement compared to the results obtained by the large eddy simulation method. The non-uniform wind speed has significant influences on the vertical， lateral， and torsional buffeting responses of the main beam， and the non-uniform wind attack angles can also affect the torsional response of the main beam. The vertical and lateral buffeting response spectra at the mid-span point under the non-uniform wind speed are obviously higher than those under the uniform wind speed， while the differences of torsional buffeting response spectra at the mid-span point between the non-uniform wind speed and the uniform wind speed are not distinct.