Abstract: Continuous conductivity imaging system of EH-4 is the update numeral instrument with electromagnetic method. With regard to the spectral leak problem of EH-4 system caused by Fourier transform of limited time and discrete sampling, the frequency spectrum characteristics of EH-4 signals in Fourier transform under the different windows and their influence on signal analysis are discussed. Different windows indicate the characteristics of the different sides of signal, and have the different merits and defects respectively. Analysis and interpretation of EH-4 signals done in different windows will be complete and authentic.