The invention relates to a generating set sub-synchronous oscillation suppression method adopting a full-controlled variable current device. The method uses the variable quantity of a rotating speed signal of a generating set as a control quantity, and performs filter, phase shift, proportional amplification and operation processing on the variable quantity of the rotating speed signal to acquire a control signal for controlling a variable current power unit by using a voltage synchronization signal as standard, then the full-controlled variable current device generates a sub-synchronous model modulation current, and the current affects the rotating speed of the generating set through a power transmission unit so as to achieve the aim of suppressing the sub-synchronous oscillation of the generating set. A controller comprises a plurality of signal processing subunits and a main control subunit, wherein each signal processing subunit comprises a filter module, a phase shift module, a proportional amplification module and an operation module; and the main control subunit accomplishes the control for the full-controlled device. The method can effectively suppress the sub-synchronous oscillation problem of a power grid system, has high response speed and high tracing precision, and can greatly improve the stability and reliability of a power grid.