Abstract: The activities of swarms of small earthquakes before the Haicheng earthquake were obviously precursory earthquake swarms. They played an important role in the prediction of the Haicheng Earthquake. Many other violent earthquakes sofar occurred in China, similar to the Haicheng earthquake, also had precursory earthquake swarms. The preliminary results obtained from the study of the precursory earthquake swarms by using the data of S-wave show that the polarization properties of S-wave were quite stationary.