According to airworthiness requirement, the effect of windmilling imbalance loads on civil aircraft structures should be evaluated. An evaluation method for strength analysis of civil aircraft structures which are subjected to wind milling loads is introduced in this paper, including static strength, fatigue strength and damage tolerance. Considering the characteristics of the methods, which have been accepted by airworthiness authority, some appropriate improvements are made. Then an evaluation approach for aircraft structural strength under windmilling loading is presented. Details about some significant aspects of this approach, such as flight profile, modification coefficient, dynamical modeling, selection principle of positions to be analyzed and failure criteria, are provided. The advantages of this evaluation method are also presented. Brief description about the application of this method in aircraft type design is given, and some improvement suggestions are provided.