It has been found that control performance of a UPFC is affected by variations of its control operating point in two folds. Firstly at different control operating points， there may exist no joint set of UPFC controllable parameter regions. This means that there is no guarantee that fixed-parameter UPFC can operate effectively at different control operating points. Secondly at certain control operating points， there exist no UPFC controllable parameter regions at all. This is due to the interactions of UPFC SISO（single input， single output） controllers because UPFC in fact forms a multivariable system and multiple SISO cannot always operate successfully. In order to solve those two problems in the design of UPFC to ensure its robustness to the variations of control operating points， this paper proposes a novel scheme of coordinated design of UPFC by using variable-parameter open-loop decoupling control. The proposed scheme is presented in details and validation in an example power system installed with a UPFC is given.