The current research analyzed the flutter response of the Stonecutters Cable-Stayed Bridge in Hong Kong, which has a twin deck configuration, under the effect of wind. The aerodynamic instability response of the bridge steel deck of the main span is mainly the focus of the current project. Initially, a complete finite element bridge model was created in ABAQUS finite element software, representing all the structural elements of the Stonecutters Cable-Stayed Bridge in a lumped mass bridge model. The natural frequencies and the vibration modes were validated against the data available in the literature at first. Secondly, the effect of the mean wind loading for wind speeds between 35 m/s and 211 m/s were determined. The vertical and horizontal displacements and the torsional angle at mid-span are indicated to determine the bridge performance under mean wind load. Moreover the flutter instability was modeled based on Scanlan’s theory and the response of the bridge model at several different locations along the main and the side span and the top of the tower, were determined for wind speeds of 35 m/s and higher, where this critical aerodynamic instability is expected to occur. In addition, the responses of the bridge under natural wind data were also determined by applying a wind speed recorded data to the bridge model. Finally, the critical flutter wind speed and the flutter frequency were determined by Fast Fourier Transform in MATLAB program. The flutter onset wind speed was also determined.