This paper concerns the use of relative gain array (RGA) for analyzing the interactions among the wind power plant voltage controller and power system traditional voltage stability controllers. RGA analyses for both static and dynamic voltage stability controls are carried out based on the multi-input multi-output (MIMO) transfer function matrix J v (s). By means of the singular value and RGA, the dynamic voltage stability and their controller interactions are analyzed and the dynamic voltage stability control loop selection can be realized. A multi-machine power system with a wind power plant is simulated for the demonstration of the proposed approach. The proposed approach takes the advantages of the classical static voltage stability analysis and the modern multi-variable feedback control theory. This proposed approach is simple and can be easily implemented into large power systems with distributed wind power plant voltage controllers.