An advanced and unique finite-element-based aerodynamic model that can be used to analyze both flutter instability and buffeting response in the time domain is presented. The equation of motion in the time domain is expressed in modal-coordinate state-space form. The frequency-dependent flutter derivatives are transferred into the time-dependent rational function, through which the coupling effects of three-dimensional aerodynamic motions under gusty wind can be accurately considered. The buffeting forces are considered through the quasi-steady formulation together with the appropriate aerodynamic admittances. A multidimensional autoregressive moving average model is used to simulate the fluctuating wind velocities along the bridge. The numerical examples are performed on the three-dimensional finite-element model of the Akashi Kaikyo Bridge with a main span length of 1,990 m. The results show that good agreement in the buffeting response is obtained between the analytical results and the experimental results of the full-bridge aeroelastic model in the windtunnel test. Various significant parameters affecting buffeting response are also extensively investigated.