The utility model discloses a resonance monitoring devices of ultra -high voltage transformer, include: gather each phase electric current of ultra -high voltage transformer output, be each looks current switchover data signal's electric current collector, each phase voltage of gathering ultra -high voltage transformer output is each looks voltage conversion data signal's voltage collector, calculate each mutually respectively with same looks data signal's electric current and the corresponding fundamental wave of voltage, the value of each subharmonic and a harmonic, if it reaches and predetermines the corresponding first parameter of adjusting of resonance intensity to have the value of the fundamental wave of certain looks, the value of each subharmonic reach with the number of times of presetting resonance intensity and the harmonic corresponding second parameter of adjusting respectively, between the value of harmonic reach and predetermine the corresponding third of the resonance intensity parameter of adjusting, then confirm ultra -high voltage transformer output certain produce the controller of predetermineeing resonance intensity resonance mutually. The utility model provides a technical scheme can detect the emergence of the single -phase resonance of ultra -high voltage transformer accurately.