The design of cable supported bridge with long span is challenging due to the sensitivity of the dynamic excitation. The aerodynamic instability caused by fluttering can severely affect the safe operation. An application of indicial function to the flutter analysis in time domain is applied to the Great belt East Bridge for both completed and erection stage. The nonlinear least square method was used to extract the aerodynamic indicial parameters for flutter analysis in time domain. The geometric nonlinearity is considered through the nonlinear dynamic analysis. The results showed the good agreement with the wind tunnel test and the validity of the indicial function as well as the important role of the geometrically nonlinear analysis during deck erection.