Recently, more and more practical applications show that in excessively noisy electromagnetic environment, using wavelet transform (WT) only may bring waveform distortion. The Fast Fourier Transform (FFT) can suppress sinusoidal interference without concerning the signaltonoise ratio (SNR). Unfortunately, the FFT is almost helpless in suppressing white noise. Thus, combining the advantages of the two transforms, a new method to suppress both white noise and sinusoidal interference is presented. At first, the automatic threshold FFT is used to suppress sinusoidal interference partially and to raise the SNR. Then WT is used to suppress both the residual sinusoidal interference and white noise. Simulation results and practical applications demonstrate that this method can extract partial discharge (PD) signals effectively in excessively noisy electromagnetic environment.