Abstract: In this paper, A method of time domain analysis of acoustical emission prior to earthquakes is presented. The method is based on the statistical characterization of the zero-crossing of the acoustical emission. The expected number of the zero-crossing within a given time interval may be regarded as a spectral parameter of the signal. The time variant structure of the environmental acoustical emission can be analysed by this method. A mathematical description and primary experimenter results are given in this paper.