The infrasonic signals (the P-t curve, the direction and horizontal velocity of the wave and the three-dimensional dynamic frequency spectrum) stimulated by seven strong earthquakes in May 2000 were introduced. The results over a year are as follows: (1) 10 days or so before the occurrence of a strong earthquake, the precursory infrasound of the earthquake with strong amplitude and measurable direction can often be observed. The characteristics of the spectrum are: the amplitudes of precursory infrasound increase from weak (10-20Pa) to strong (40-80Pa) or even stronger; the final periods become very wide (2-65min); their waveforms are distinctly different from those of meteor showers and strong winds, (2) The maximal amplitude of the precursory infrasound measured is related not only to the magnitude of earthquake, but also to the distance and the depth of the epicentre and some other factors. (3) The generating and propagating mechanism of the precursory infrasound of the earthquake was preliminarily explained. (4) If the directions of two tripartite arrays intersect, the location of the epicentre can be predicted. Therefore measurements of precursory infrasound could become a new and more effective method of the imminent prediction of strong earthquakes.
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