The utility model discloses a harmonic suppressor for suppressing a passive-type reactive power compensation device. The harmonic suppressor comprises a three-phase transformer with an iron core, a capacitor, a diode rectifier bridge, a direct current resistor, a damping diode and an IGBT field effect transistor. The three-phase transformer with an iron core comprises a UA phase transformer UTA with an iron core, a UBB phase transformer UTB with an iron core and a UC phase transformer UTC with an iron core. After the harmonic suppressor is connected with a circuit, the problem of amplification of special harmonic waves or inter-harmonics by a passive-type reactive power compensation device and a power grid can be solved, and the problem is solved that the passive-type reactive power compensation device is out of service which is caused by that the practical harmonic wave amount is too large because of addition or replacing of user devices.