Accounting for the flexibility of the blade and tower of the horizontal axis wind turbine, based on modal analysis method, the coupling dynamic equations of the blade and tower were obtained to simulate the dynamic behaviour of the complete system. Numerical solution of the dynamic equations was presented by applying the linear acceleration method. Adopting the proposed model, the dynamic responses of a 1.25MW wind turbine operating in steady wind were calculated. The results indicate that the presented structure dynamic response analysis model can correctly reflect the effects of external excitements to the structure deformation and load. It can also be seen from the simulation results that the flexible structures of large-scale wind turbine undergo considerable deformation during operation, and reasonable load results can be obtained when taking into account the former two order modes.