Abstract: For the high-noise，nonlinear and non-stationary characteristics of low-frequency signal in impact failure process of coal，introducing HHT time-frequency analysis method into low-frequency signal analysis，denoising and time-frequency disposing of low-frequency signal was finished with this method.Results showed that EMD decomposition and reconstitution could not only denoise signal，but also describe well nonlinear，non-stationary and pulsing characteristics of low-frequency electromagnetic signal.Spectrogram of lowfrequency magnetic signal could clearly show dynamic variation of energy with time and frequency.From spectrogram，dominant frequency of low-frequency magnetic signal was within 0～40Hz and its duration was less than 2s.Compared with Fourier transform and wavelet analysis，HHT method has higher time and frequency resolution，whole time-frequency localization and could well describe time-varying characteristic of electromagnetic signal，which is effective method for time-frequency analysis of electromagnetic signal.