The invention provides a smooth switching method for the control modes of a static var compensator SVC. A controller of the static var compensator SVC comprises a comparison unit, a PID control unit,a mode control unit and a trigger pulse generator. The comparison unit comprises a reference voltage input interface and an SVC bus high-voltage side voltage input interface. The mode control unit comprises a manual control input interface, an automatic control input interface and a control mode interface. The method comprises the following steps: I, adding the reference voltage input interface ofthe comparison unit to a reference voltage input control unit; II, adding the manual control input interface of the mode control unit to a manual mode input control unit; and III, improving the function of a PID controller, and adding the control mode interface and a Bsd-out interface to the input end. The technical scheme provided by the invention can ensure that the SVC can be smoothly switchedbetween control modes without causing impact to the system.