This paper presents an improved fuzzy synthetic model that is based on a real-time condition assessment method of a grid-connected wind turbine generator system (WTGS) to improve the operational reliability and optimize the maintenance strategy. First, a condition assessment framework is proposed by analyzing the monitored physical quantities of an actual WTGS with an electrically excited synchronous generator (EESG) and a full-scale converter. To examine the variable speed operational performances, the dynamic limits and the deterioration degree functions of the characteristic variables are determined by analyzing the monitoring data of the WTGS. An improved fuzzy synthetic condition assessment method is then proposed that utilizes the concepts of deterioration degree, dynamic limited values and variable weight calculations of the assessment indices. Finally, by using on-line monitoring data of an actual 850 kW WTGS, real-time condition assessments are performed that utilize the proposed fuzzy synthetic method; the model’s effectiveness is also compared to a traditional fuzzy assessment method in which constant limited values and constant weights are adopted. The results show that the condition assessment that utilizes the improved method can predict the change of operating conditions and has a better coherence with real operating conditions than that of a traditional fuzzy assessment method.