The span of a cable-stayed bridge is getting longer due to the current achievement of technology. On the contrary, this design is susceptible to surrounding wind flow that can generate aeroelastic instability. For instance, the catasthropic collaps of Tacoma Bridge. In this instability, the interaction of the elastic, inertia and aerodynamic forces must be taken into account. Therefore, aeroelastic study is needed. The following case study considers 2-D and 3-D analysis on divergence, flutter aeroelastic instability, and structure response. They apply the solution of eigenvalue problem, K, and Runge-Kutta methods, respectively. In addition, the influences from variation of wind-nose shapes are investigated and critical condition on both as-built and free-standing half- structure are compared. The divergence and flutter characteristic of structural stability can be obtained, together with its structural respons. The analysis of 2-D and 3-D structure provide a good results, The wind-nose of deck with aerodynamically shaped give higher critical divergence speed. The investigation also reveals that the Great Belt bridge deck section is the most insensitive to the flutter, therefore has the highest critical flutter speed, 172,4 m/s. Furthermore, most critical condition of structure is the bridge as built under life load.