The invention discloses a wide-range controllable transformer-based power oscillation suppressor comprising bidirectional thyristors. The power oscillation suppressor consists of a controllable transformer, power units, a measurement and control module, a cross phase conversion module, filtering capacitors, an input voltage transformer, an output voltage transformer and an output current transformer; and the input end of the power oscillation suppressor is connected with a bus 1 and the output end of the power oscillation suppressor is connected with a bus 2. According to the power oscillation suppressor, an additional two-phase winding is in tandem connection with each phase tap of the wide-range controllable transformer, and meanwhile, the four thyristors are additionally arranged to change a breakover direction of the cross-phase windings, so that a phase position and an amplitude value of the controllable transformer are changed to the maximum extent, and active power and reactive power adjustment can be realized. When power oscillation in a power grid appears, according to a control rule, the active power and the reactive power of the power oscillation suppressor are dynamically adjusted, so that the power grid can be stabilized as soon as possible. The power oscillation suppressor has characteristics of low cost and high reliability, and can improve the stability of the power grid and the damping of a system.