Abstract: In the 500kV ultra-high voltage built-in ultra-high frequency partial discharge detection, there is high-frequency composite noise that interferes and masks the partial discharge signal, making it difficult to obtain accurate partial discharge waveforms. This paper focuses on the wideband extended circuit model of the circuit and proposes a wideband extended circuit noise control method based on fractional order filtering system. The effectiveness, stability, and reliability of this method in controlling high-frequency composite noise in UHF partial discharge detection have been verified through laboratory experiments and on-site environmental tests.