In order to improve the stability of whole wind turbine system with blade and tower coupled，a new method，which constructs and solves optimization model to optimize the structure of wind turbine，is developed. The method takes minimizing system vibration as the objective function，and diameter and thickness of tower as decision variables. It constructs optimization model using strength，deformation and mass，etc.，as constraints. Interior penalty function technique is applied to solve the optimization model，and Campbell diagram is employed to analyze the system stability. The formulation and solution method are applied to a 2 MW horizontal axis wind turbine，and the stability of the whole turbine is greatly improved and tower mass is reduced by 13%，which demonstrates the proposed method not only contributes to theory research but also leads to great benefits in practice.