Abstract: The plant electrical signal is very complex，with non-steady-state and time-varying.Before acquiring a useful signal，original signal needs to be preprocessed and acquired signal is strictly limited to useful frequency band.First，the signal is low-pass filtered to keep high frequency noise；and then notch filter is used to eliminate existence of the 50 Hz frequency interference caused by active equipment in test environment.The wavelet de-noising method is used to process acquired signals，so that noise or other unnecessary information can be separated more easily.Through programming in MATLAB language，digital filter was designed to realize pretreatment of signal.The method of wavelet analysis was used to analyze signal，and purpose of noise reduction and interference removal was achieved，so plant electrical signal was analyzed effectively.