Abstract: Using polarization analysis method, this psper discussses Datong—Yftnggao M_s 5.8 earthquake occurred on Oct.19 of 1989.Preliminary results show that there had ever been S—wave splitting anomaly (from Sept.of 1988 to Oct.of 1989).In accordance with the orientation, northeast and north—northeast, of principal compressive stress in North China,the dominant orientation of the fast S—wave polarization is northeast before the earthquake.From this,the orientation of vertical parallel arranging cracks in the crust is the same.The results show, that abnornal phenomenon of s—wave splitting might be found before the strong earthquake from the digital records of local earthquakes (epicentral distance is about 200 km).It increases the possibility of that we use S-wave splitting method into earthquake prediction.Finally, the different characters of S—wave polarizaetions in and out of the S—wave window are simply discussed.