This paper reviews the recent research on the interactions of FACTS control， especially that on the interaction of multiple control functions of a UPFC. In order to exclude the influence of setting of parameters of UPFC with the variations of its control operating points， it is proposed that the interactions of UPFC control can be studied by computing its controllable parameter regions. In the paper， the New England 10-machine 39-node power system installed with a UPFC is used to demonstrate the effectiveness of the proposed method. By computing the controllable parameter regions of the UPFC， useful conclusions about the interactions of UPFC control are obtained， that have excluded the influence of setting of parameters of UPFC.