The invention discloses a harmonic and resonance suppression device of electric railway. The harmonic and resonance suppression device comprises a hurl-slices switch, a reactor Z, a resonant detection device and a switch changeover controller, wherein the hurl-slices switch is connected to a power supply arm of a traction transformer, the reactor Z is connected in series with the hurl-slices switch and then is connected to the power supply arm of the traction transformer, an input end of the resonance detection circuit is connected with the power supply arm, an output end of the resonance detection circuit is connected with the switch changeover controller, the resonance detection circuit is used for judging whether resonance occurs in a traction network of the traction transformer or not, an input end of the switch changeover controller is connected with the output end of the resonance detection circuit, an output end of the switch changeover controller is used for generating a control signal for suppressing harmonic and resonance of the electric railway according to a detection result of the resonance detection circuit and issuing a control instruction to the hurl-slices switch. The invention also provides a harmonic and resonance suppression method of the electric railway. The harmonic and resonance suppression device has the beneficial effects of low loss, wide harmonic suppression spectrum and no reactive overcompensation.