Using the correlation coefficient method，it studies shear wave splitting on the basis of the records of a small earthquake swarm in the“Huoshan seismic window”． The results show that the preponderant polarization of fast shear wave is NEE． It accords with the regional predominant direction of principal compressional stress． The time delay would basically increase before strong shocks． However，it was observed that the time delay abruptly decreased immediately before one strong shock． It is consistent with the conclusion that long-term stress accumulation and short-term stress relaxation exist before earthquakes． It is significant for the short-term earthquake prediction that the time delay will decrease before strong earthquakes． The result suggests the parameters of shear wave splitting may reflect the dynamic change of region stress field and provide useful information for the study of stress field and earthquake prediction．