Abstract: The buffeting performance of the longest double-cantilever state of Zhanjiang Bay Bridge under construction is investigated trough a wind tunnel test of aeroelastic model. The result shows that the normal wind case may not be the most unfavorable case for the buffeting responses of long-span cable-stayed bridges. The variation of the buffeting responses is not monotonous with the increase of wind yaw angle, and the maximal values may occur at a wind yaw angle between 0° and 15°. The buffeting responses grow with the increase of wind speed according to a quadratic curve approximately, and the contribution of the fundamental natural mode to the buffeting responses takes a dominant portion. It is also found that the longitudinal buffeting response at the tower top of the longest double-cantilever state is significantly larger than that of the free-standing tower state, and the variation patterns of the longitudinal response with the wind yaw angle are different for these two structural states. The comparison between experimental and computed results shows that a reasonable theoretical prediction of buffeting responses can be attained so long as the determination of aerodynamic parameters, such as aerodynamic admittance functions, is solved properly.