Abstract: In order to study the buffeting response of long-span cable-stayed bridges under downburst, based on the measured downburst wind speed at Chishi Bridge site, the time-varying mean wind speed of downburst was extracted by wavelet transform method, and the modulation function with time was obtained. The Kaimal spectrum was taken as the target spectrum, and the turbulence wind speed at the bridge site was simulated by harmonic superposition method. The simulated fluctuation wind speed was modulated and the time history of the simulated downburst wind speed was obtained. On this basis, the static wind response and nonlinear buffeting response of the long-span cable-stayed bridge in construction condition under downburst wind field and atmospheric boundary layer (ABL) wind field were calculated respectively. The results show that the wind speed of downburst at bridge site is abrupt. The time history of wind speed of the simulated downburst is in good agreement with the measured wind speed. The time-varying power spectrum amplitude of simulated fluctuation wind under downburst wind field is obviously larger than that of simulated fluctuation wind under ABL wind field. When downburst wind at bridge deck height is the same as atmospheric boundary layer wind speed, and considering the time-varying mean wind effect of downburst, the maximum value of the static wind effect of bridge girder end is about 1.20 times ofthat of the static wind effect of bridge girder end calculated by the 10-minute mean wind speed; the RMS values of buffeting responses of bridge girder end and tower top under downburst wind are respectively larger than that of buffeting responses of bridge girder end and tower top under ABL wind field, and the maximum ratio is about 2.8.