The invention discloses a device and a method for stimulating subsynchronous oscillation of an electric power system, and belongs to the field of stabilizing and controlling of the electric power system. The device comprises a counter, a time-variant frequency signal generator, a sinusoidal wave signal amplitude generator and a sinusoidal wave signal generator. The counter, the time-variant frequency signal generator and the sinusoidal wave signal generator are sequentially connected, and the sinusoidal wave signal amplitude generator is connected with the sinusoidal wave signal generator. The method includes: the step 1: the time-variant frequency signal generator generates subsynchronous frequency signals which change according to a set time-varying function; the step 2: the sinusoidal wave signal amplitude generator generates subsynchronous frequency sinusoidal wave signal amplitudes; the step 3: the sinusoidal wave signal generator receives the subsynchronous frequency signals and the subsynchronous frequency sinusoidal wave signal amplitudes, and generates subsynchronous frequency sinusoidal wave signals. By the device and the method, problems that actual oscillation has strong destructiveness and is difficult to control are solved, and effective measurements and methods are provided for actual devices for simulation analysis and subsynchronous oscillation.