For the sake of easing the threat to the safe and stable operation of power system, control performance of static var compensator, widely used in cluster wind farms, and their triggering process of voltage overshoot are analyzed detailedly in this paper. The combined action of response lag and physical property defects, produces malposition compensation effect in SVC, which supports no effective reactive power output during voltage drip, while exports surplus reactive power during recovery process after fault resection. In order to overcome the limitations of SVC control performance, an additional locking control embedded in the SVC controller, is put forward, which comes into action merely under the condition of lower voltage.The judging criteria of SVC locking control and reoperating after shutting is given, to avoid malposition compensation, to effectively reduce high voltage threat triggered by SVC, thus ensuring the safety and stability of wind farm. Lastly, simulation has verified the effectiveness of the proposed control strategy. In addition, this tip offers some guidance for late construction and operation of wind farm.