Abstract: Three-pylon cable-stayed bridges with two main spans are more flexible. The vibration modes of the bridge are close to each other. Based on the multimode coupled buffeting analysis, coupled behavior in buffeting response of three-pylon cable-stayed bridges is investigated in this paper. Buffeting response of a three-pylon cable-stayed bridge is analyzed at design wind speed by multimode coupled analysis method and one-mode SRSS method, respectively. The coupled effect is neglected in one-mode SRSS (Square Root of Sum of Squares) method. RMS (Root Mean Square) and PSD (Power Spectral Density) of buffeting response by the two methods are compared with each other. In order to indicate the coupled relations among the analyzed modes, the evolution of buffeting response with number of modes is analyzed. It is shown that there is significant coupled behavior in buffeting response of three-pylon cable-stayed bridges. The coupled interaction among analyzed modes can increase the buffeting response. The coupled effect of buffeting response should be not neglected in the refined analysis of long-span bridges.