Based on an analysis of basic control strategy for variable-speed pitch controlled wind turbine driven generator system， an improved control strategy of enlarging the transition region is proposed to mitigate the harmful effects caused by controller switch near the rated power point， such as power fluctuation and sudden load change. A three-controller smooth transition scheme is designed to fulfill the optimal tracking to the improved control strategy. The operation characteristics of the generator system with the improved control strategy are simulated on the MATLAB simulation platform， and the results prove the correctness and effectiveness of the improved control strategy.